In short. Melasma triggers include ultraviolet light, visible light, heat, hormonal change, some medicines and thyroid problems, and most people have two or three acting at once. Ultraviolet is largely blocked by window glass but visible light is not, which is why a face can darken during a week spent indoors.
Key points
- Ultraviolet light is the best-known trigger, but visible daylight also drives pigment.
- Window glass blocks most ultraviolet light and does not block visible light.
- Heat acts separately from light, and inflamed skin stimulates the pigment cells.
- Pregnancy, hormonal contraception, hormone replacement and the menopause all change the signal.
- Rapid darkening, or darkening within weeks of a new medicine, needs medical review.
Ultraviolet light and visible light
Ultraviolet light is the best-known trigger and the one most people protect against. It is not the only one. Visible light, the ordinary daylight that comes through window glass and the glare from a bright sky, also drives pigment production in melasma. Ultraviolet is largely blocked by glass; visible light is not. That is why a face can darken during a week spent indoors, why tinted protection matters as much as sunscreen, and why a hat and a seat away from the window are part of treatment rather than extras.
Heat as a separate trigger
Heat is a trigger in its own right, separate from light. Cooking over a hot wok, saunas, steam rooms, hot yoga, a fever, and long hours in a hot car can all darken melasma. So can any treatment that inflames the skin. The mechanism is the same as the one that makes a laser risky: inflammation in the skin stimulates the pigment cells, and melasma is what an over-reaction looks like.
Which hormonal changes matter?
Pregnancy is the classic setting for melasma, and it is not the only one. Hormonal contraception, hormone replacement, the years around the menopause, and some treatments for other conditions all change the hormonal signal reaching the skin. The patches may appear during the change or fade afterwards; either way, the hormonal history is one of the most useful things to bring to an assessment.
| Trigger | What it is | Where it appears in ordinary life | What helps |
|---|---|---|---|
| Ultraviolet light | The best-known trigger, driving pigment production | Time outdoors in sun | Sunscreen and covering the face |
| Visible light | Ordinary daylight, including light that passes through glass | Indoors beside a window, glare from a bright sky | Tinted protection, a hat and a seat away from the window |
| Heat | A trigger separate from light | A hot wok, saunas, steam rooms, hot yoga, a fever, long hours in a hot car | Recognising it as a trigger in its own right |
| Inflammation | Inflamed skin stimulates the pigment cells | Any treatment that inflames the skin | Treating inflamed skin as a trigger |
| Hormones | A changed hormonal signal reaching the skin | Pregnancy, hormonal contraception, hormone replacement, the years around the menopause | Bringing the hormonal history to an assessment |
| Medicines and thyroid | Some medicines increase light sensitivity; thyroid problems are more common with melasma | A new medicine, or fatigue and weight change | Asking for both to be checked |
Medicines, thyroid and general health
Some medicines make the skin more sensitive to light, and thyroid problems appear more often in people with melasma than in the population at large. Neither is common, and neither should be assumed, but both are worth checking when pigmentation appears or darkens quickly, or when it comes with fatigue, weight change or other general symptoms. This is the part of the assessment that a beauty counter cannot do.
Why do triggers add up over a season?
Most people who develop melasma have two or three factors overlapping in the same period: a sunny summer, a hormonal change, and a run of long days beside a window. Writing down when the patches first appeared, and what else was happening that year, is often more useful than any product history.
When should a doctor review the pigmentation?
The darkening is rapid, or it started within weeks of a new medicine. The pigmentation comes with fatigue, weight change or feeling generally unwell. One patch differs from the others, or is changing while the rest are stable.
Sources
- American Academy of Dermatology: patient information on melasma
- British Association of Dermatologists: patient information leaflet on melasma
- Cochrane Library: systematic reviews on treatments for melasma
Internal links
Frequently asked questions
Does screen light really affect melasma, or is that an exaggeration?
Screen light itself is weak compared with daylight, but the screen is not what matters most — the bright window beside it is. Sitting in daylight for hours, even indoors, delivers the visible light that melasma responds to. The practical answer is tinted protection and a change of position when you can, rather than a screen filter.
Should I avoid exercise and cooking because of the heat?
Not avoid, but plan around. Heat is a genuine trigger, and a hot kitchen or a hot yoga class can darken melasma. Cooking in a cooler kitchen, keeping the face away from steam and direct heat, and cooling the skin afterwards are reasonable adjustments. Stopping exercise entirely is not necessary and would cost you more than it gains.
Can melasma start years after my last pregnancy?
Yes. Pregnancy is a common first setting, but the same pigment response can be triggered later by a change in hormonal contraception, hormone replacement around the menopause, or a period of intense light exposure. The tendency is there; the trigger is what changes, and it is often something in the last year rather than the last decade.
Risks & Limitations
- Melasma is chronic and relapsing. Treatment lightens it and maintenance keeps it lighter; it does not cure it.
- Sunlight and visible light can bring the patches back after a good result, so photoprotection is permanent.
- Aggressive laser treatment can worsen melasma and cause rebound darkening in some patients.
- Pregnancy, breastfeeding and hormonal treatment change what is safe, and must be discussed before any plan starts.
When to Seek Care
- A pigmented patch that is new, changing, asymmetrical or bleeding needs assessment to exclude other diagnoses.
- Darkening is rapid, or follows a new medicine or hormonal treatment.
- Skin becomes inflamed, blistered or persistently red after a lightening product or procedure.
- Pigmentation appears with fatigue, weight change or other general symptoms.
References & Further Reading
- American Academy of Dermatology (AAD) — patient guidance on this condition
- International League of Dermatological Societies (ILDS) — global standards of care
- National Institute for Health and Care Excellence (NICE, UK) — relevant guidance
- Cochrane Library — systematic reviews on the treatments discussed here
This page is patient education, not medical advice, and it does not cite individual studies. Discuss your own case with a qualified clinician. To arrange an assessment at Chongqing West District Hospital, see Contact & Consultation.