I have been using topical finasteride spray for hair loss and I read that it can cause breast cancer. This has frightened me and I have stopped the treatment. Is that risk actually real?

Hello, Ana,

I completely understand why you decided to stop taking it after reading something like that. The word 'cancer' immediately raises concerns, but in this case it is important to separate what we know scientifically from what is often interpreted based on information found online.

There is currently no scientific evidence demonstrating that using topical finasteride on the scalp causes breast cancer in women.

That does not mean we should claim the risk is absolutely zero, because long-term safety studies specifically in women using topical finasteride are still limited.

However, there is also currently no scientific basis for telling a patient that using topical finasteride will cause breast cancer.

What exactly is finasteride?

Finasteride blocks an enzyme called 5-alpha-reductase, which is responsible for converting part of the testosterone into dihydrotestosterone, or DHT.

DHT plays an important role in the progressive miniaturisation of the hair follicle that we observe in androgenetic alopecia.

By reducing DHT production around the follicle, we aim to slow down that miniaturisation and preserve, for as long as possible, the ability to produce higher-quality hair.

Why use it as a spray?

Precisely because we seek to achieve a sufficient concentration of the medication in the scalp while reducing, as much as possible, exposure to the rest of the body.

Topical finasteride can be partially absorbed and produce some reduction in circulating DHT, which means that 'topical' does not mean the medication remains exclusively on the skin.

However, with appropriate formulations, systemic exposure can be considerably lower than with oral treatment.

So where does the concern about breast cancer come from?

The relationship between finasteride and breast cancer has been discussed for years because the modification of androgen metabolism can produce hormonal changes, and because some cases of breast cancer were reported in men using oral finasteride.

However, a case report does not in itself prove that the medication caused those cancers.

And, above all, we cannot directly extrapolate those cases observed in men taking oral finasteride to a woman using a topical formulation on the scalp.

To date, we do not have evidence demonstrating an increase in breast cancer in women as a result of using topical finasteride.

Should I stop the treatment then?

I would not discontinue it solely because you read online that 'finasteride causes breast cancer'.

What I would do is review your individual situation.

I want to know your age, the concentration you are using, the amount applied daily, how long you have been using it, and whether there is any significant personal or family history of breast cancer.

If a woman has previously had hormone-dependent breast cancer, is receiving hormonal oncological treatment, or is in a situation of particularly high risk, the decision deserves an individualised assessment and, where appropriate, coordination with her oncologist or gynaecologist.

Not because we know that topical finasteride causes a recurrence, but precisely because the available data in these populations are insufficient to act carelessly.

There is another much more well-established precaution: pregnancy.

This point is truly essential.

Finasteride must not be used during pregnancy due to its anti-androgenic action and the potential risk to the development of a male foetus.

In a woman of childbearing age, we must carefully assess the possibility of pregnancy and the necessary contraceptive measures before recommending the treatment.

Furthermore, with topical formulations we must ensure that other people — especially a pregnant woman — do not accidentally come into contact with the product while it is still wet on the scalp.

My recommendation

Do not be afraid of a medication simply because you come across an alarming association on the Internet.

But do not use a hormonal treatment for years without medical supervision either.

Topical finasteride is a tool that can be very valuable in certain types of androgenetic hair loss, and it allows us to try to act on one of the mechanisms responsible for follicular miniaturisation.

With the evidence currently available, we cannot state that topical finasteride increases the risk of breast cancer in women.

If the treatment was working and you have stopped it solely out of this concern, I would speak with the doctor who prescribed it before discontinuing it permanently.

In medicine, this is precisely what we must do: weigh up the benefit, understand the demonstrated risks, acknowledge what data are still lacking, and not turn a theoretical possibility into a certainty that science has not proven.