Scabies or scabiosis: symptoms, transmission, and treatment. Why does the itching get worse at night?

What is scabies or scabiosis?

Scabies, also known as scabiosis, is not caused by a bacterium, a virus, or a fungus, but by a parasite: Sarcoptes scabiei var. hominis. It is a microscopic mite adapted to humans. The female penetrates the outermost layer of the skin, the stratum corneum, and burrows small tunnels where she deposits her eggs.

In classic scabies, surprisingly, a person usually harbors only around 10 to 15 mites. However, the immune reaction to the mite, its eggs, and its byproducts can trigger extraordinarily intense itching. Therefore, the intensity of the itch does not mean that we have thousands of parasites traveling across our skin: a large part of the symptoms are due to our own immune system's response to the infestation.

What are the symptoms of scabies?

The most characteristic symptoms are intense itching, especially at night; small bumps or papules; lesions caused by scratching; fine furrows or tunnels in the skin; and similar lesions in other family members or people living in the same household.

Classic locations include the spaces between the fingers, the wrists, the armpits, the waistline, the buttocks, the genital area, and the area around the nipples. In infants and young children the distribution can be different and may also affect the head, face, neck, palms, and soles.

The burrows are particularly interesting: they can look like very fine, slightly raised, winding lines. They are, literally, the tunnel excavated by the mite within the superficial layer of the skin. However, they are not always easy to find.

Why does scabies itch so much at night?

Nocturnal itching is one of the best-known clinical signs of scabies, but we should not explain it simply by saying that 'the mite comes out at night.' The reality is more complex: the pruritus is primarily due to a hypersensitivity reaction to the mite and its byproducts.

The perception of pruritus also changes according to circadian rhythms and can intensify at night due to factors such as skin temperature, inflammatory mediators, and the absence of the stimuli that distract our attention during the day. That is why a very typical account is: 'during the day I can manage it, but when I get into bed I cannot stop scratching.' Nocturnal itching does not by itself prove that scabies is present, but when associated with compatible lesions and other household members experiencing pruritus, it becomes a very important clue.

How long does it take for scabies to produce symptoms?

This is where one of the reasons it spreads so easily comes into play. In a person who has never had scabies before, symptoms can take approximately 3 to 6 weeks to appear — some sources place the interval at up to around 8 weeks. During that period, the person may be infested and transmit scabies without knowing it.

If someone has had scabies before, their immune system recognises the parasite more quickly and symptoms can appear much faster, typically within a few days. This explains a very common situation: a person starts itching today and thinks 'I was infected yesterday.' Not necessarily — the exposure may have occurred weeks earlier.

How is scabies transmitted?

The main route of transmission is direct, close, and sufficiently prolonged skin-to-skin contact. This is why it can spread between partners, people who share a bed, family members, housemates, caregivers, or people living in institutional settings.

It can also be transmitted through sexual contact, but it is worth clarifying: having scabies does not necessarily mean having acquired a sexually transmitted infection. Anyone can catch it. A quick handshake or a brief hug is generally not enough to transmit classical scabies.

Can scabies be spread through sheets, towels, or clothing?

Yes, but in classical scabies this route is less important than prolonged direct contact. Transmission can occur through clothing, towels, or bed linen recently used by an infested person, since the mite generally survives only 2 to 3 days away from human skin.

There is, however, one very important exception: crusted, or hyperkeratotic, scabies. In this form the number of mites can be enormous, and the contaminated environment becomes far more significant.

Does scabies mean poor hygiene?

No. This is one of the myths we most need to dispel. Scabies can affect children, adults, older people, and individuals with excellent hygiene, at any socioeconomic level. The fundamental factor is having had sufficient contact with an infested person.

Situations of close cohabitation or overcrowding facilitate transmission, but scabies is not evidence of 'dirtiness.' The WHO estimates that at least 200 million people may have scabies at any given time worldwide.

How can I tell whether I really have scabies?

The diagnosis is essentially clinical: we look for nocturnal itching, a characteristic distribution, compatible lesions, and affected contacts. The presence of burrows considerably increases suspicion. In certain cases we can draw on dermoscopy.

When confirmation is needed, microscopic examination of material obtained from a lesion can also be performed to identify mites, eggs, or remnants of the parasite. However, not all patients require a microscopic test to establish the diagnosis.

What conditions can be confused with scabies?

Many: atopic dermatitis, contact dermatitis, papular urticaria, insect bites, folliculitis, eczema, or itching from other causes. This is why context matters enormously. Not every episode of nocturnal itching is scabies, and not every itchy spot should automatically be treated with permethrin.

How is scabies treated?

The treatment has two main objectives: eliminating the mite from the patient and preventing contacts from reinfesting them. The two most commonly used medications are 5% permethrin (topical) and ivermectin (oral).

5% Permethrin

It is one of the reference topical treatments. It must be applied correctly over the entire indicated skin surface, not only on top of the visible bumps. In adults, standard protocols include application from the neck downward, paying particular attention to areas that are easily overlooked: between the fingers, under the nails, the wrists, the armpits, the navel, the genital area, skin folds, the buttocks, and the feet.

It is left on for the indicated length of time — usually overnight — and then washed off. It is frequently necessary to repeat the application approximately one week later: the CDC describes applications spaced approximately one week apart, and the WHO notes that repeating the treatment improves efficacy by eliminating mites that may have hatched subsequently. In young children and in certain situations, the area to be treated may also include the head and neck, so instructions must be tailored to the patient's age and individual circumstances.

What about oral ivermectin?

Ivermectin is another highly effective option. In classic scabies, when given orally, two doses of 200 micrograms per kilogram are typically administered 7 to 14 days apart, depending on the protocol and the patient's characteristics. Why two doses? Because ivermectin does not reliably eliminate all eggs, and the second dose helps to eliminate any newly hatched mites.

The choice between permethrin and ivermectin depends on factors such as age, pregnancy, weight, drug interactions, the type of scabies, the feasibility of correctly applying the topical treatment, and the epidemiological situation. The safety of oral ivermectin has not been established in the same way for pregnant women and children weighing less than 15 kg, and it should therefore not be used indiscriminately in these groups.

Permethrin or ivermectin: which is better?

There is no universal answer. Both can be highly effective when correctly indicated and used. For some people, an oral treatment is more straightforward; for others, we prefer topical permethrin. And there are special situations — crusted scabies in particular — in which an intensive combination of topical and oral treatment may be necessary. The choice must be individualized.

Why does scabies treatment fail so often?

This is probably the most important part of the article. In many cases, there is no true pharmacological resistance, but rather a problem of strategy. For example: only the person who was itching was treated; a household member was infested but still asymptomatic; the treatment was not repeated correctly; the cream was not applied to all the necessary areas; the hands, nails, feet, or genitals were overlooked; there was renewed contact with an untreated person; or the residual itching was interpreted as treatment failure, triggering an unnecessary succession of treatments.

That is why treating scabies means treating the entire chain of transmission as well.

Do household contacts need to be treated even if they have no symptoms?

This point is fundamental. The WHO recommends that household members be treated simultaneously, even when they do not yet have symptoms, precisely because there is an asymptomatic period during which they may already be infested. Depending on the situation, we must also evaluate sexual partners, people who share a bed, and other close contacts.

There is little point in carrying out the treatment perfectly if that same night the person is re-exposed to a close contact who is still infested.

What should I do with the sheets and clothing?

There is no need to turn the house into an operating theatre or to fumigate it. Environmental measures should be reasonable and targeted. Clothing, sheets, and towels that have recently been in contact with the skin can be washed in hot water and dried at a high temperature; the CDC notes that temperatures above 50 °C for 10 minutes destroy mites and eggs.

Items that cannot be washed can be kept inside a sealed bag for several days — practical recommendations range from at least 72 hours to one week. It is generally not necessary to throw away the mattress, fumigate the entire home, or use environmental insecticides; in fact, the CDC advises against pesticide sprays and environmental fumigation for scabies control.

Why do I still have itching after treatment?

This is possibly the question that causes the most anxiety. The patient carries out the treatment correctly and, a week later, is still itching and thinks: 'I still have scabies.' Not necessarily: the treatment may have eliminated the mites, but our immune system can still react for a period of time to the remains of the parasite and to the inflammatory process it has triggered.

Itching can persist for several weeks after effective treatment. This is often referred to as post-scabietic pruritus. Therefore, persistent itching does not automatically mean active scabies.

So, how do we suspect that treatment has truly failed?

We should reassess particularly when new burrows appear, new typical lesions develop, live mites can be demonstrated, or when the condition continues to progress rather than improving gradually. The CDC recommends reassessment if pruritus persists 2 to 4 weeks after treatment or if new burrows or new papular lesions appear. The key is to distinguish persistent infestation from residual inflammation once the mite has been eliminated.

What is crusted scabies, or Norwegian scabies?

It is a completely different form in terms of parasite burden and contagiousness. In classic scabies we typically speak of 10 to 15 mites; in crusted scabies there may be thousands, hundreds of thousands, or even millions of mites. The skin develops thick, hyperkeratotic, crusted, and scaly plaques, and curiously the itching may even be mild or entirely absent.

It is more common in certain patients: immunocompromised individuals, elderly people, patients with conditions that impair the perception of itching or scratching, and certain institutionalized patients. And it is extraordinarily contagious.

How is crusted scabies treated?

Not like conventional scabies. It usually requires intensive treatment combining topical permethrin and oral ivermectin, with repeated regimens adapted to the severity of the case. We sometimes also use keratolytic treatments to facilitate the penetration of the scabicide through the crusts. Furthermore, due to its enormous transmission capacity, it is essential to identify and treat contacts and to control the environment.

Can scabies become infected?

Yes. Intense itching causes scratching, scratching breaks down the skin barrier, and bacteria that normally live on our skin — such as Staphylococcus aureus or streptococci — can then penetrate and cause impetigo, superinfection, cellulitis, and, in exceptional cases, more serious complications.

If increasing pain, pus, extensive yellowish crusts, warmth, progressive redness, or fever appear, we should consider a bacterial superinfection.

Can I get scabies again after recovering?

Yes. Having had scabies does not provide lasting protective immunity, so you can become reinfested. In a reinfestation, symptoms may appear much more quickly because the immune system already recognizes the mite. This is why, when it seems as though 'scabies always comes back,' we should ask ourselves whether there is truly treatment resistance, or whether we are dealing with a reinfestation, an untreated contact, incorrect application, or simply post-scabietic itch.

When should I seek medical advice?

A medical evaluation is advisable when there is newly onset intense nocturnal itching; several household members with symptoms; lesions between the fingers, on the wrists, or on the genitals; suspicious burrows; persistent symptoms after treatment; signs of bacterial infection; pregnancy; a young child who is affected; immunosuppression; or suspected crusted scabies.

Particularly in care homes, institutions, or settings with numerous contacts, quickly identifying the first case can prevent a full outbreak.