Why does melasma worsen in summer?
Melasma is a pigmentation disorder characterised by symmetrical brown or greyish-brown patches on the face (forehead, cheekbones, upper lip), caused by overactivation of the melanocytes (the cells that produce melanin). It is chronic and recurrent in nature, and summer concentrates all of the factors that trigger it.
The first and best known is ultraviolet radiation: both UVB rays (which affect the epidermis) and UVA rays (which penetrate as far as the dermis) stimulate melanin production. However, scientific research in recent years has identified two other aggressors equally relevant to melasma: high-energy visible light (particularly the blue-violet spectrum between 400–500 nm) and the heat generated by infrared radiation. Summer amplifies all of these simultaneously, producing a multiplicative effect.
Added to this is the hormonal factor: the oxidative stress generated by sun exposure acts with greater intensity in women with elevated oestrogen levels (whether due to hormonal contraceptives, hormone replacement therapy, or pregnancy), which explains why melasma affects women of childbearing age disproportionately.
Photoprotection is essential, but it must be the right kind.
Photoprotection is the cornerstone of melasma management: without it, no depigmenting treatment maintains its results. However, not every sunscreen is sufficient for melasma.
A randomised clinical trial published in 2022 in Photodermatology, Photoimmunology & Photomedicine compared two sunscreens with the same SPF 50 applied alongside hydroquinone: the group that used the sunscreen with visible light filters achieved a significantly greater reduction in the MASI index (the standard melasma severity scale) than the group using conventional UV protection. A randomised prospective study from 2025 confirmed these results specifically during the summer period.
The scientific recommendations with the greatest support are:
- SPF 50+ broad-spectrum coverage of both UVA and UVB. This is non-negotiable: in a study of 200 pregnant women who applied SPF 50+ daily, fewer than 3% developed melasma, compared to the usual 15–50% in that risk group.
- Formulations containing iron oxides (tinted or coloured photoprotection). Iron oxides are the only ingredients with demonstrated efficacy against high-energy visible light, with attenuation rates exceeding 93%. An untinted sunscreen, even at SPF 50+, does not provide this protection.
- Reapplication every 2 hours during direct sun exposure, and after each swim or bath.
The most common mistake: relying solely on sunscreen.
Applying sunscreen is necessary, but not sufficient. The scientific literature identifies other modifiable factors that contribute to the worsening of melasma in summer:
- Avoiding sun exposure during the central hours of the day (between 10 a.m. and 4 p.m.) is just as important as sunscreen. The combined use of hats or caps also reduces the radiation load on the skin.
- Heat alone (saunas, very hot baths, hot kitchens, etc.) can activate melanocytes independently of solar radiation. This explains why some people notice a worsening of their melasma even without direct sun exposure.
- A review of hormonal treatment is relevant in women whose melasma appeared or worsened upon starting oral contraceptives. In such cases, a joint assessment with gynaecology can have a real clinical impact.
- Topical antioxidants (vitamin C or niacinamide) applied in the morning help to neutralise the oxidative damage generated by visible and infrared light, complementing the action of the sunscreen.
What can I do to keep melasma under control in summer?
Although melasma does not resolve definitively, its progression is highly modifiable with the right measures:
- Use a tinted SPF 50+ sunscreen containing iron oxides every morning, including on cloudy days and indoors near windows.
- Reapply every 2 hours during sun exposure and after each swim or bath.
- Complement with a hat and photoprotective clothing when outdoors.
- Avoid intense heat and the central hours of the day.
- Incorporate vitamin C or other topical antioxidants into the morning skincare routine.
- Maintain dermatological follow-up during summer, particularly if an active depigmenting treatment is underway.
In conclusion, summer need not be synonymous with relapse. With the right tools and a personalised plan, melasma can remain stable even during the months of greatest sun exposure. If you have melasma and are concerned about being unable to keep it under control as summer approaches, a specialist dermatologist can help you design a personalised plan that makes a real difference.
