Tamoxifen is a SERM — it blocks estrogen in some tissues but acts like it in skin. Why melasma follows, and how treatment differs.
Hello. This is Dr. Lee Yumin of MeSOnBom Clinic.
Treating melasma is considered one of the most difficult areas in dermatology.
Dozens of patients come to us each day with pigment conditions, and what gives doctors most pause are vascular and stubborn melasma.
Over years of treating pigment I have noticed one clear trend in practice.
Patients whose melasma was triggered by hormonal change or hormonal treatment are increasing sharply.
It appears most often in women in their thirties and forties who have been through pregnancy and birth, long-term users of oral contraceptives, and middle-aged women on hormone therapy for menopause.
The relationship between hormones and melasma is medically clear: when estrogen levels rise, melanocytes are stimulated and melasma develops.
But in longer conversations with patients I meet cases that this formula alone cannot explain.
Those are patients taking the anti-hormonal drug tamoxifen long term after breast cancer surgery.
When I explain to patients on tamoxifen that the medication may be behind their melasma, they often question it.
"Doctor, isn't tamoxifen an estrogen antagonist? If it suppresses female hormones, shouldn't melasma get lighter instead?"
That is a perfectly logical question.
Tamoxifen binds to estrogen receptors in breast cancer cells and acts as an antagonist, blocking estrogen from proliferating those cells.
But there is a more complex mechanism at work.
Tamoxifen is medically classified as a selective estrogen receptor modulator (SERM).
That is, in some tissues it suppresses estrogen, while in others — skin, uterus, bone — it acts instead like an estrogen agonist.
Dermatological studies published in Portugal and the Philippines have found that tamoxifen acts in a manner similar to estrogen on normal melanocytes in the skin, strongly stimulating melanin production and triggering melasma.
Patients on tamoxifen usually report melasma becoming noticeable around five years into treatment.
They often say it was fine yesterday and suddenly covered their face.
But melasma does not appear overnight. Hormonal stimulation continues at the base of the skin because of the medication, and with UV exposure and ageing accumulating alongside it, it progresses slowly beneath the surface.
It is only recognised when it passes the point at which makeup can cover it. It often settles darkly and widely in a long band beneath the eyes.
The difficulty is that melasma caused by tamoxifen is far harder to treat than ordinary melasma, because the skin environment itself has broken down.
Fine vessels frequently proliferate beneath the melasma, continuously feeding the melanocytes, and the skin barrier — the basement membrane — is commonly weakened.
So trying to break up the pigment forcefully with a strong laser readily produces a rebound in which the melasma darkens instead.
Meaningful improvement therefore requires treating the pigment gently, with minimal stimulation — pico toning for example — while always combining regenerative treatment such as Sylfirm X or Rejuran to stabilise the abnormal vessels in the dermis and restore the skin barrier.
Unfortunately, melasma does not improve immediately when the course of medication ends.
Over five to nearly ten years of taking the drug, the skin has already settled into an environment in which melasma grows readily.
Many such patients have persistent redness from numerous fine vessels or a generally darker tone, so the response to treatment is also slower than in normal skin.
Speed of response: normal skin > skin after stopping tamoxifen > skin still on tamoxifen.
What is clear is that skin responds far more favourably to treatment after the course has finished than during it.
So setting aside impatience and treating consistently matters most.
In oncology treatment at a university hospital, it is hard to receive a detailed explanation of melasma as a side effect of tamoxifen.
It is not prominent on the list of major side effects.
Where tumour treatment is directly tied to survival, pigmentation — a relatively cosmetic matter — inevitably comes second.
But I see every day in clinic that for women climbing the mountain of breast cancer, the dark melasma they meet in the mirror each morning goes beyond appearance and becomes real psychological stress and low mood.
The most important thing I want to say to patients is that completing cancer treatment safely comes before everything else.
Marks on the skin can be removed slowly and safely with your doctor afterwards, even if it takes longer.
I hope this offers some comfort and a clear medical answer to those quietly struggling with darkened skin from tamoxifen. Thank you.
Our medical team will advise you based on your skin condition.
