Why does melasma return as soon as the skin sees the sun?

Brown spots, poorly defined, appearing on the cheekbones, forehead, or upper lip, often during pregnancy or after starting birth control pills, which darken as soon as the sunny days return: this is melasma.

It's not just a simple sunspot. It's a hyperpigmentation with a dual cause – hormonal and solar – which explains both its occurrence and its stubborn tendency to return. Understanding this completely changes the treatment strategy.

Without strict sun protection, no melasma treatment is effective in the long term.

A pigment factory that's too active

In melasma, melanocytes, the cells that produce pigment, are overactive. The phenomenon involves a dialogue between melanocytes, keratinocytes, dermal blood vessels, and certain inflammatory cells. Ultraviolet radiation damages the DNA of epidermal cells and triggers the release of signals that prompt melanocytes to produce more melanin. In affected skin, estrogen receptors are highly expressed, making these cells particularly reactive to hormones and sun. This dual sensitivity distinguishes melasma from common pigmentation.

Sun and hormones, the two triggers

The sun is the number one contributing factor. But ultraviolet light is not the only cause: visible light, especially the blue spectrum also emitted by the sun, stimulates pigmentation in pigmented skin. This is why a classic transparent sunscreen is not always enough. On the hormonal side, pregnancy, which gives it the nickname "mask of pregnancy," and estrogen-progestin contraceptives are recognized triggers. This hormonal dependence explains why melasma primarily affects women of childbearing age and why it can fade after childbirth or stopping the pill, without necessarily disappearing on its own.

Not to be confused with a scar

Melasma differs from post-inflammatory hyperpigmentation, the spots that remain after a pimple, insect bite, or irritation. The latter is a localized reaction to a specific aggression and tends to fade on its own over time. Melasma, on the other hand, is diffuse, symmetrical, maintained by hormones and sun, and it recurs. This distinction is essential: an overly aggressive treatment, intended to "erase" the spot, can actually inflame the skin and permanently worsen melasma.

The active ingredients that have proven their worth

Sun protection is non-negotiable, and a tinted sunscreen containing iron oxides is a real asset here: these pigments block a portion of visible light. A randomized trial showed that a sunscreen also covering visible light was better at preventing relapses than a UV-only sunscreen.

Tranexamic acid, derived from an amino acid, works by inhibiting signals that stimulate melanocytes. Taken orally, by prescription, it has shown a significant reduction in melasma severity in trial syntheses; it is also available for topical application. 20% azelaic acid targets hyperactive melanocytes and is a well-tolerated local option, with efficacy comparable to classic depigmenting references. Niacinamide usefully complements the routine by limiting the transfer of pigment to surface cells, with a favorable tolerability profile.

Why it recurs

Melasma is a chronic condition: it fades, but it doesn't disappear permanently. The slightest unprotected exposure, a new pregnancy, or the resumption of hormone therapy can reactivate pigmentation. This is why management is considered long-term, with daily photoprotection maintained even in winter and even on cloudy days, and continued use of active ingredients after initial improvement. Expectations must remain realistic: the goal is a clear and lasting lightening, not a guaranteed disappearance.

The Paradermia approach

Our pharmacist builds a routine adapted to your phototype and skin sensitivity, based on a simple principle: photoprotection first, then active ingredients. Specifically, a broad-spectrum sunscreen also covering visible light, applied every morning, followed by gentle depigmenting active ingredients like azelaic acid or niacinamide, introduced gradually to avoid irritating the skin and potentially triggering inflammation. When melasma is extensive or resistant, we recommend seeking medical advice, as oral tranexamic acid requires a prescription.

Frequent questions

Can melasma disappear on its own after pregnancy?
It can fade after childbirth or stopping hormone therapy, but it rarely disappears completely on its own. Without rigorous photoprotection, it tends to persist or return.

Is a transparent sunscreen sufficient?
Not always. Visible light also stimulates pigmentation. A tinted sunscreen containing iron oxides provides better protection against this part of the spectrum and helps prevent relapses.

Is melasma the same as spots after a pimple?
No. The spot that follows a pimple is localized post-inflammatory hyperpigmentation, which often fades on its own. Melasma is diffuse, symmetrical, maintained by hormones and sun, and it recurs more easily.