The skin speaks: 25 cutaneous signs that may reveal internal diseases

This does not mean that every spot, pimple, or mole is a sign of serious illness. The majority of common skin lesions are benign or correspond to conditions that are intrinsic to the skin itself.

However, certain changes — especially those that appear suddenly, are extensive, persist over time, or are accompanied by other symptoms — can offer important clues.

In medicine, observing the skin is not solely about diagnosing skin lesions. It can also help us understand what is happening inside the body.

In this guide, we will explain 25 skin manifestations that may be linked to internal diseases: what they mean, when it is advisable to investigate them, and which medical specialty may be involved.

1. Why can an internal disease manifest in the skin?

The skin receives blood, nutrients, hormones, and immune signals from throughout the body.

When a systemic disturbance is present, changes may occur in pigmentation, superficial circulation, sebum production, epidermal renewal, hair growth, or nail structure.

For example, liver disease can cause jaundice and itching; a thyroid disorder can alter the texture of the skin and hair; and certain metabolic conditions may be accompanied by characteristic lesions in the skin folds.

There are also autoimmune diseases that simultaneously affect the skin, joints, muscles, kidneys, or other organs.

In some cases, the skin manifestation is one of the first signs. In others, it appears once the disease is already known.

The diagnostic significance depends on three aspects:

• What the lesion looks like: color, shape, texture, location, and distribution.

• How it evolves: whether it appeared suddenly, is growing, resolves on its own, or persists.

• What other symptoms are present: fatigue, fever, weight loss, pain, digestive disturbances, or general changes.

An isolated skin lesion rarely allows for the diagnosis of an internal disease without additional evaluation.

2. General table: 25 skin signs that may be linked to internal diseases

Important: this table shows clinical associations, not diagnostic equivalences. The presence of a lesion does not necessarily mean that the person has the condition mentioned.

Metabolic and endocrine diseases

3. Skin tags: why do small wart-like growths appear on the neck and armpits?

Skin tags, also known as soft fibromas or skin tags, are small benign lesions, generally soft and skin-colored or slightly pigmented.

They frequently appear on the neck, armpits, groin, and other skin folds.

They are very common, and their presence in isolation does not necessarily indicate any disease.

However, when they are numerous, they may be associated with obesity, insulin resistance, and metabolic syndrome.

What is their relationship with insulin?

Insulin resistance occurs when certain tissues respond less effectively to this hormone.

The body can compensate by producing larger amounts of insulin.

Hyperinsulinemia may play a role in cell growth and proliferation processes, although the exact relationship with skin tags does not allow them to be used as a diagnostic test.

When should they be investigated?

When numerous skin tags appear — especially in the presence of abdominal overweight, a family history of diabetes, hypertension, or metabolic disorders — it may be reasonable to assess cardiometabolic risk.

Depending on the clinical context, blood glucose, glycated haemoglobin (HbA1c), lipid profile, and other factors may be evaluated.

Having skin tags does not mean having diabetes, but in certain individuals it can be an opportunity to review their metabolic health.

4. Acanthosis nigricans: why does the skin on the neck darken and thicken?

Acanthosis nigricans is characterised by a darkening and thickening of the skin, typically with a velvety texture.

It appears particularly in:

• The neck.

• The armpits.

• The groin.

• Other skin folds.

Its most frequent association is with insulin resistance and metabolic disorders.

It can be observed in people with obesity, type 2 diabetes, or polycystic ovary syndrome.

Can it be related to cancer?

There are rare forms of acanthosis nigricans associated with internal neoplasms.

They tend to attract particular attention when they appear suddenly, are extensive, or affect unusual areas — especially in adults with other systemic symptoms.

But it is essential to keep things in perspective: the vast majority of acanthosis nigricans cases are not caused by cancer.

5. Xanthelasmas and xanthomas: what is their relationship with cholesterol?

Xanthelasmas are yellowish plaques that typically appear around the eyelids.

Xanthomas are lipid deposits that can occur in other locations, presenting in a variety of clinical forms.

Certain types of xanthomas are closely associated with significant disorders of lipid metabolism.

Eruptive xanthomas, for example, can appear in situations of severe hypertriglyceridemia.

Tendinous xanthomas can point toward certain hereditary dyslipidemias.

Xanthelasmas, on the other hand, can also appear in people with normal cholesterol levels.

What should we do?

Assess the lipid profile and cardiovascular risk factors when indicated.

It is not enough to remove the lesion for cosmetic reasons if there is an underlying metabolic disorder that requires treatment.

6. Hypothyroidism: when the skin becomes dry and hair begins to fall out

The thyroid gland regulates numerous metabolic processes.

When it produces an insufficient amount of thyroid hormones, manifestations such as the following may appear:

• Dry, rough, or cold skin.

• More brittle hair or diffuse hair loss.

• Decreased sweating.

• Brittle nails.

• Facial swelling in certain cases.

Fatigue, constipation, cold intolerance, or weight changes may also be present.

None of these signs is exclusive to hypothyroidism.

If the clinical context warrants it, measuring TSH and, where appropriate, free T4 can assist in diagnosis.

7. Hyperthyroidism: warm skin, sweating, and hair changes

When there is an excess of thyroid hormones, the skin may feel warmer and more moist.

Increased sweating, fine hair, or hair loss may appear.

In certain patients with Graves' disease, thyroid dermopathy may develop, classically located in the pretibial region.

If these signs are accompanied by palpitations, tremor, weight loss, or heat intolerance, a thyroid disorder should be considered.

8. Addison's disease: why do some people develop generalised dark pigmentation?

Primary adrenal insufficiency, known in certain cases as Addison's disease, can cause hyperpigmentation.

It can be observed particularly in:

• Hand folds.

• Scars.

• Areas subject to friction.

• Oral mucosa.

This pigmentation is related to the increase in ACTH and peptides derived from its precursor.

It may be accompanied by intense fatigue, weight loss, hypotension, nausea, and a craving for salt.

The combination of new hyperpigmentation with hypotension and general symptoms warrants medical evaluation.

If severe vomiting, extreme weakness, confusion, or circulatory collapse occur, an adrenal crisis must be ruled out, as it constitutes a medical emergency.

Liver, kidney, and digestive tract diseases

9. Jaundice: why do the skin and eyes turn yellow?

Jaundice appears when the concentration of bilirubin in the body increases.

It may manifest as a yellowish coloration of the skin and, especially, of the sclera of the eyes.

Among its possible causes we find:

• Liver diseases.

• Obstruction of the bile ducts.

• Certain processes involving accelerated destruction of red blood cells.

Jaundice should not be confused with a simple cosmetic alteration of skin tone.

When should we be concerned?

New-onset jaundice requires prompt medical evaluation.

If it is accompanied by fever, intense abdominal pain, confusion, or general deterioration, it may indicate an urgent situation.

10. Generalized itching without lesions: can an internal disease be the cause?

Yes.

Generalized pruritus without primary skin lesions is one of the situations in which we must consider systemic causes.

This does not mean that every patient with itching has an internal disease.

Dry skin, dermatitis, and other dermatological causes are common.

But when the itching persists, affects large surface areas, and we cannot find a clear cutaneous explanation, it may be appropriate to broaden the investigation.

Possible internal causes

• Hepatobiliary diseases: especially those that produce cholestasis.

• Chronic kidney disease: particularly in advanced stages.

• Thyroid disorders: both hypothyroidism and hyperthyroidism.

• Hematological diseases: such as polycythemia vera and, less frequently, certain lymphomas.

• Iron deficiency: in some patients.

The study will depend on the clinical history and physical examination.

Persistent itching is not necessarily resolved by changing creams. Sometimes we need to investigate its origin.

11. Spider angiomas and palmar erythema: can they indicate liver disease?

Spider angiomas are small vascular dilations with a central point and radiating branches.

They can appear in healthy individuals and in physiological situations such as pregnancy.

However, when they are numerous, especially alongside other signs, they may be associated with chronic liver disease.

Palmar erythema can also be observed in certain liver conditions, although it is not specific.

Other findings that may point toward liver disease include jaundice, bruising, ascites, and certain nail abnormalities.

None of these signs in isolation confirms cirrhosis.

12. Chronic kidney disease: how can it affect the skin?

Chronic kidney disease, especially when advanced, can produce cutaneous manifestations.

Among the most common we find:

• Intense dryness.

• Persistent itching.

• Pigmentation changes.

• Lesions secondary to scratching.

In advanced situations, less common manifestations may appear.

Pruritus associated with chronic kidney disease is a recognised clinical problem and can considerably affect quality of life.

If there is clinical suspicion, evaluation may include creatinine, estimated glomerular filtration rate, and urinalysis, depending on the context.

13. Dermatitis Herpetiformis: a dermatological manifestation of coeliac disease

Dermatitis herpetiformis is an autoimmune skin condition closely related to coeliac disease.

It typically produces intensely pruritic lesions, frequently distributed symmetrically over:

• Elbows.

• Knees.

• Buttocks.

• Scalp.

The vesicles can be difficult to observe because scratching breaks them.

It is not an infection caused by the herpes virus, despite its name.

Its diagnosis may require a skin biopsy with direct immunofluorescence and investigation for celiac disease.

It is not advisable to eliminate gluten before completing the diagnostic tests without medical guidance, as it may hinder their interpretation.

14. Erythema nodosum: when painful nodules appear on the legs

Erythema nodosum presents as inflammatory and painful nodules, typically on the front of the legs.

It may be accompanied by fever, fatigue, or joint pain.

Among its possible associations are:

• Inflammatory bowel disease.

• Sarcoidosis.

• Certain infections.

• Pregnancy.

• Other inflammatory conditions.

Not all cases allow a specific cause to be identified.

The physical examination and accompanying symptoms guide the necessary tests.

15. Pyoderma gangrenosum: can it be linked to digestive or haematological diseases?

Pyoderma gangrenosum is a rare inflammatory disease that can cause painful ulcers, often with a rapid course.

It may be associated with:

• Inflammatory bowel disease.

• Inflammatory arthritis.

• Certain haematological diseases.

Its diagnosis requires careful evaluation and the exclusion of other causes of ulceration.

A painful, rapidly progressing ulcer should not be treated as a simple wound without first establishing its cause.

Autoimmune and rheumatological diseases

16. Lupus: what does a butterfly-shaped rash mean?

Systemic lupus erythematosus is an autoimmune disease that can affect different organs.

One of its well-known cutaneous manifestations is the malar erythema, which affects the cheeks and the bridge of the nose.

Photosensitivity, specific skin lesions, oral ulcers and hair loss may also appear.

However, not every butterfly-shaped redness is lupus.

Rosacea and other conditions can produce a similar appearance.

When suggestive lesions are present alongside joint pain, significant fatigue, fever, urinary changes or other systemic symptoms, a targeted evaluation may be necessary.

17. Dermatomyositis: when the skin can reveal a muscle disease

Dermatomyositis is an inflammatory disease that can affect both the skin and the muscles.

Among its characteristic skin signs we find:

• Gottron's papules: lesions over certain joints of the hands.

• Heliotrope erythema: a violaceous discoloration around the eyelids.

• Photosensitive lesions: on the neckline, back and other exposed areas.

Some patients present proximal muscle weakness, with difficulty getting up from a chair, climbing stairs or raising their arms.

There are also forms with cutaneous manifestations without evident muscle weakness.

Can it be associated with cancer?

In certain adults, dermatomyositis is associated with an increased risk of neoplasia.

For this reason, once the diagnosis is confirmed, the workup for possible associated conditions should be individualized according to age, clinical features, and risk factors.

This does not mean that all people with dermatomyositis have cancer.

18. Raynaud's phenomenon: why do the fingers turn white or blue in the cold?

Raynaud's phenomenon consists of episodes of vasospasm affecting mainly the fingers.

Color changes may occur, frequently triggered by cold or stress.

In some patients there is a primary form, with no associated systemic disease.

In others it may be related to autoimmune diseases, especially those affecting connective tissue.

We should pay attention when it appears for the first time in adulthood, is highly asymmetric, causes ulcers, or is accompanied by skin hardening and other symptoms.

19. Systemic sclerosis: why does the skin on the fingers harden?

Systemic sclerosis is an autoimmune disease characterized by vascular alterations and fibrosis.

It can cause:

• Thickening and hardening of the skin.

• Swollen or stiff fingers.

• Raynaud's phenomenon.

• Telangiectasias.

• Digital ulcers.

It can also affect the digestive tract, lungs, heart, and other organs.

For this reason, recognizing certain skin manifestations can contribute to an earlier diagnosis.

Blood disorders and vascular conditions

20. Petechiae and purpura: what do red or purplish spots that do not disappear when pressed mean?

Petechiae are small spots caused by the extravasation of blood.

Purpura encompasses larger hemorrhagic skin lesions.

Unlike many superficial vascular inflammatory lesions, these spots generally do not disappear when pressure is applied.

Among its possible causes we find:

• Platelet disorders.

• Coagulation disorders.

• Vasculitis.

• Infections.

• Vascular fragility.

• Other systemic diseases.

Palpable purpura may point toward small vessel inflammation, although it requires differential diagnosis.

When is it urgent?

The appearance of petechiae or purpura together with fever, general malaise, hypotension, or rapid progression requires urgent evaluation.

21. Frequent bruising: can it indicate a blood disorder?

Bruises can appear from minimal trauma, especially when skin fragility is present.

However, when they are extensive, spontaneous, frequent, or accompanied by gum bleeding, epistaxis, or other symptoms, further investigation may be necessary.

Among the possible causes are platelet disorders, coagulation abnormalities, and certain hematological diseases.

Evaluation may include a complete blood count and coagulation tests, depending on the clinical history.

22. Paleness, brittle nails, and anemia: what is the connection?

Anemia can cause pallor of the skin and mucous membranes.

When iron deficiency is present, some patients develop nail brittleness and, occasionally, koilonychia, characterized by concave-shaped nails.

Diffuse hair loss may also occur.

However, these findings are not exclusive to iron deficiency.

Diagnosis requires appropriate tests, which may include a complete blood count, ferritin, and other iron metabolism parameters.

The interpretation of ferritin must also take into account the presence of inflammation.

23. Diffuse hair loss: when should we look for an internal cause?

Hair loss does not always correspond to a disease exclusive to the hair follicle.

Telogen effluvium can appear following situations such as:

• Major acute illness.

• Surgery.

• Physiological stress.

• Rapid weight loss.

• Nutritional deficiency.

• Thyroid disorders.

• Iron deficiency in certain patients.

Hair loss usually manifests weeks or months after the triggering event.

Not everyone experiencing hair loss needs an extensive panel of tests.

The clinical history, physical examination, and pattern of alopecia determine which tests may be useful.

24. Clubbed fingers: what conditions should we consider?

Acropachy, also known as digital clubbing, consists of a change in the shape of the tips of the fingers and nails.

It can appear in certain pulmonary, cardiac, digestive, or hepatic diseases.

There are also familial or idiopathic forms.

Its recent onset, especially when accompanied by a persistent cough, breathing difficulties, or other systemic symptoms, warrants evaluation.

It is not an exclusive sign of lung cancer, although some thoracic neoplasms may be associated with it.

Nutritional diseases and deficiencies

25. Lesions around the mouth and on the extremities: could zinc be deficient?

Zinc deficiency can cause a characteristic dermatitis, frequently located around body orifices and in acral areas.

It may be accompanied by alopecia, diarrhea, and impaired wound healing.

There are hereditary and acquired forms.

Acquired forms may be related to malabsorption, inadequate nutrition, or other clinical conditions.

Treatment requires adequately confirming or substantiating the suspicion and correcting the underlying cause.

It is not advisable to take zinc supplements at high doses for prolonged periods without medical indication, as they can cause adverse effects, including copper deficiency.

The skin and certain oncological diseases

26. Can the sudden appearance of numerous brown lesions indicate an internal cancer?

There is a classic clinical sign known as the Leser-Trélat sign.

It describes the abrupt appearance of multiple seborrheic keratoses, often with rapid growth in number or size.

Seborrheic keratoses are very common benign lesions, especially with advancing age.

They usually present a warty or waxy surface and a characteristic appearance of a lesion stuck onto the skin.

What is its relationship with cancer?

The Leser-Trélat sign has been described in association with certain internal neoplasms, especially some adenocarcinomas.

However, the validity of this association as a true paraneoplastic syndrome continues to be a matter of debate.

This is due, among other reasons, to the fact that both seborrhoeic keratoses and neoplasms increase in frequency with age.

Having many seborrhoeic keratoses does not mean having cancer.

What deserves special attention is a truly sudden, extensive and progressive eruption, particularly when it is accompanied by unexplained weight loss, digestive symptoms or other general manifestations.

Are moles, skin tags and seborrhoeic keratoses the same thing?

No.

This distinction is fundamental.

We must not confuse a sudden appearance of seborrhoeic keratoses with an increase in true moles.

27. What other cutaneous manifestations can be associated with internal neoplasms?

There are rare cutaneous paraneoplastic syndromes.

Among them we find:

• Dermatomyositis associated with neoplasm: in certain adult patients.

• Malignant acanthosis nigricans: a rare form, often with sudden onset and significant extent.

• Necrolytic migratory erythema: a characteristic manifestation that may be associated with glucagonoma, a rare neuroendocrine tumour.

• Sweet's syndrome: a neutrophilic dermatosis that, in a minority of cases, may be related to haematological diseases.

• Bazex's acrokeratosis paraneoplastica: a rare skin condition associated with certain neoplasms.

These entities are important for medical diagnosis, but they do not represent common causes of spots, eczema, or small benign lesions.

The aim of knowing about them is not to suspect cancer at every skin change, but to recognise specific clinical patterns that warrant a targeted investigation.

How to interpret cutaneous signals

28. What accompanying symptoms increase the significance of a lesion?

The interpretation changes when cutaneous manifestations are accompanied by general symptoms.

Among the findings that deserve particular attention, we find:

• Involuntary weight loss.

• Persistent fever.

• Unexplained night sweats.

• Intense, newly onset fatigue.

• Joint pain or muscle weakness.

• Persistent digestive changes.

• Jaundice.

• Unexplained bleeding.

• Edema.

• Respiratory disturbances.

• Sudden and extensive appearance of lesions.

These symptoms do not confirm a specific disease, but they may affect the need for and urgency of medical evaluation.

29. Which specialist should I consult depending on the manifestation?

The initial evaluation can be carried out by a primary care physician or an internal medicine doctor, who will guide the workup and decide whether the involvement of another specialty is necessary.

Not all patients need to be referred directly to several specialists.

A well-directed initial clinical assessment can prevent unnecessary consultations and tests.

30. What tests may be requested when we suspect an internal disease?

There is no universal blood panel for all skin lesions.

Depending on the symptoms and physical examination, the physician may consider:

The choice of tests must be individualized.

For example, ordering autoantibodies without adequate clinical suspicion can generate positive results of uncertain significance and unnecessary concern.

Likewise, it is not recommended to order tumor markers indiscriminately in the presence of non-specific skin lesions.

31. When should we go to the emergency room?

Some skin manifestations require immediate attention, especially when accompanied by significant systemic symptoms.

These include:

• Petechiae or purpura with fever and general malaise. They may appear in serious illnesses that require urgent evaluation.

• Jaundice accompanied by fever, intense abdominal pain, or confusion. It may indicate a significant hepatobiliary complication.

• Rapidly progressing violaceous or necrotic lesions. These may be related to vascular, infectious, or other serious conditions.

• Skin changes accompanied by difficulty breathing, loss of consciousness, or circulatory deterioration. These require urgent medical attention.

• Intense new-onset muscle weakness, especially with difficulty swallowing or breathing. This requires immediate assessment.

The urgency depends on the overall clinical picture, not solely on the appearance of a spot.

Frequently asked questions

32. Does having many skin tags mean I have insulin resistance?

Not necessarily.

There is an association between numerous skin tags and certain metabolic factors, but these lesions do not allow for a diagnosis of insulin resistance.

The workup depends on personal history and risk factors.

33. Can itching without spots be a liver disease?

Yes, in some cases.

Pruritus without primary lesions can be associated with hepatobiliary, renal, endocrine, or hematological conditions, among others.

However, dry skin and other benign causes remain common.

If the itching is persistent or unexplained, it is worth having it evaluated.

34. Do dark patches on the neck indicate diabetes?

They may correspond to acanthosis nigricans, a condition frequently associated with insulin resistance.

However, not every pigmentation of the neck is acanthosis nigricans, nor does everyone who has it have diabetes.

35. Can hair loss indicate an internal disease?

Yes.

In some cases it can be related to thyroid disorders, iron deficiency, systemic diseases, or physiological stress.

However, there are numerous primary hair-related causes, which is why it is important to identify the pattern of alopecia.

36. Does the appearance of many moles mean I have cancer?

No.

Melanocytic nevi, skin tags, and seborrhoeic keratoses are different types of lesions.

The sudden appearance of multiple seborrhoeic keratoses has been described in connection with the Leser-Trélat sign, but its association with cancer is controversial and does not constitute a diagnosis.

New or changing moles should be evaluated based on their individual characteristics.

37. Is removing a skin lesion enough to solve the problem?

It depends on the cause.

Removing a skin tag or a xanthelasma may resolve the visible lesion, but it does not correct a possible associated metabolic disorder.

Likewise, treating only the itch with a cream will not resolve a systemic disease if that is the underlying cause.

That is why it is important to distinguish between treating the skin manifestation and treating its root cause.

38. Do all people with skin lesions need blood tests?

No.

Most skin problems can be assessed through an adequate clinical history and physical examination.

Complementary tests should be ordered when there is a reasonable indication.

Running extensive tests without a specific clinical suspicion does not guarantee better care.

Conclusion: the skin can be a window into our internal health

A spot, a nail change, hair loss, or persistent itching may seem like purely skin-related problems.

And many times they are.

But under certain circumstances, the skin can provide important information about metabolism, hormones, the liver, the kidneys, the blood, or the immune system.

Medicine is about recognising when a manifestation requires only local treatment and when we need to look further.

Not everything that appears on the skin is a skin disease. Sometimes, the skin is the first organ to warn us that something is happening inside the body.

The goal is not to cause alarm at every small lesion, but to correctly interpret the signals, avoid hasty diagnoses, and act when there are signs that justify a medical evaluation.

Informational medical content. The associations described do not allow individual diagnoses to be established without a clinical assessment. Tests and referrals must be tailored to each patient.