Melasma: What May Be Influencing Your Skin

If you’ve dealt with melasma, you already know the drill: broad-spectrum SPF, tinted sunscreen, maybe a dermatologist-prescribed cream, and still those symmetrical brown patches across your cheeks, forehead, or upper lip keep coming back. Melasma is notoriously frustrating precisely because it’s so often treated as a purely cosmetic, purely topical problem. Lighten it, protect it, repeat. And while sun protection and topical care absolutely matter, they only address what’s happening on the skin, not what’s driving your melanocytes, the pigment-producing cells in your skin, to overreact in the first place.

Melanocytes don’t just randomly decide to overproduce pigment. They respond to signals: light, heat, hormones, inflammatory messengers, and stress chemistry circulating through your body. For many people, especially those whose melasma is stubborn, treatment-resistant, or keeps resurfacing no matter how diligent the skincare routine, it’s worth asking what upstream systems might be sending those signals. This article covers the triggers most people already know about, briefly, and then goes much deeper into three that get far less attention in mainstream melasma content: chronic stress and cortisol, hormonal shifts, thyroid dysfunction, and mold/mycotoxin exposure.

What Melasma Is, Briefly

Melasma is a common acquired hyperpigmentation condition marked by symmetric, irregularly bordered brown-to-gray-brown patches, most often on sun-exposed facial skin. The classic patterns are cheeks, forehead, upper lip, nose, and chin.

It disproportionately affects women, particularly during reproductive years. At its core, melasma reflects melanocytes that have become hyperactive, but current research describes it as more than an isolated pigment-cell problem: it involves crosstalk between melanocytes, keratinocytes, blood vessel cells, inflammatory signaling, and the skin’s deeper connective tissue. In other words, it’s a whole-tissue phenomenon, not a single rogue cell type  which is part of why purely topical treatment often has a ceiling.

The Triggers Everyone Already Knows About

UV and visible light are the most well-established environmental triggers for melasma. UVB stimulates melanin production directly, UVA penetrates deeper and drives oxidative stress in skin cells, and — less widely known — visible light in the blue-violet range can also trigger pigmentation via light-sensing receptors (opsins) on melanocytes, particularly in darker skin types. This is why tinted, iron-oxide-containing sunscreens (which block visible light, not just UV) tend to outperform plain mineral or chemical sunscreens for melasma specifically.

Heat appears to be an independent contributor, separate from light exposure. Think hot yoga, saunas and hot summer temps have been associated with more severe melasma in some research.

Pregnancy and hormonal shifts are the other classic triggers — hence the nickname “the mask of pregnancy” (chloasma). Estrogen and progesterone both appear to play a role: melasma-affected skin shows increased estrogen receptor expression, and pregnancy triggers melasma in a wide range of women (estimates span roughly 15–56% of pregnancies), while hormonal contraceptives are implicated in a meaningful share of cases as well. Progesterone’s role is a bit more unclear and some data suggest it can counteract estrogen’s pigment-stimulating effects rather than add to them.

These three are core standard-of-care knowledge, and any root-cause approach still has to include sun protection and hormonal history. But they don’t explain everything. Plenty of people with diligent sun protection and no pregnancy or hormonal contraceptive use still develop or struggle to clear melasma. That’s where the next three factors come in.

Cortisol and Chronic Stress: An Underappreciated Driver

Here’s a detail that rarely makes it into melasma content but is basic endocrinology: the hormone that drives your stress response and the hormone that stimulates melanocytes come from the same biochemical family. Cortisol is released via the hypothalamic-pituitary-adrenal (HPA) axis, triggered by adrenocorticotropic hormone (ACTH). ACTH and melanocyte-stimulating hormone (MSH) are both cleaved from the same parent molecule, proopiomelanocortin (POMC). A 2007 study published in The FASEB Journal showed that POMC is secreted directly by human skin cells — both keratinocytes and melanocytes — and stimulates melanogenesis locally, meaning skin doesn’t just respond to circulating stress hormones from the adrenal glands; it can generate its own local stress-hormone signaling that feeds directly into pigment production.

Beyond that shared biochemistry, there’s a well-documented bidirectional relationship between stress and skin. A 2021 review in the Journal of Drugs in Dermatology described a “bidirectional HPA stress axis” operating locally within skin tissue — meaning skin isn’t just a passive target of circulating cortisol; it participates in its own local stress-response signaling, which influences pigmentation, inflammation, and barrier function.

None of this means melasma is “caused by stress” in a simple, direct-line way, and there isn’t yet a large clinical trial measuring serum cortisol levels specifically in melasma patients versus controls. What the current evidence supports is a plausible and biologically coherent pathway: chronic stress activates the HPA axis, HPA axis activity shares upstream signaling molecules with melanocyte stimulation, and skin itself participates in local stress-hormone production — all of which gives chronic, unmanaged stress a legitimate seat at the table when investigating persistent pigmentation, even though it’s rarely mentioned outside specialty literature.

Thyroid Disease and Melasma

The foundational study here is a 1985 paper in the Journal of Clinical Endocrinology & Metabolism, which compared 84 women with melasma to 24 controls. The researchers found thyroid disorders in 58.3% of melasma patients — roughly four times the rate seen in controls (12.5%) — and thyroid autoantibodies (a marker of autoimmune thyroid disease, like Hashimoto’s thyroiditis) in 32.1% of melasma patients versus 8.3% of controls. Notably, the association was strongest — 70% — among women whose melasma developed during pregnancy or oral contraceptive use, suggesting that estrogen and progesterone may act as triggers specifically in people who are already genetically predisposed to thyroid autoimmunity.

More recent research has largely reinforced this link. A 2019 systematic review and meta-analysis in the International Journal of Dermatology, pooling seven studies with 473 melasma cases and 379 controls, found that melasma patients had significantly higher TSH, anti-thyroid peroxidase (anti-TPO) antibodies, and antithyroglobulin antibodies than controls, along with lower T4 — a pattern consistent with subclinical or autoimmune thyroid dysfunction. The differences were more pronounced in women. The review’s authors concluded that thyroid screening, including thyroid antibody testing, may be worth considering in melasma patients, while acknowledging that causality isn’t fully established.

Mechanistically, the connection likely runs through more than one pathway: shared autoimmune predisposition (the same immune dysregulation that attacks the thyroid may also affect melanocyte regulation), the hormonal overlap between thyroid hormone and estrogen/progesterone signaling, and possibly TSH’s direct effects on skin cells, which express TSH receptors.

Mold, Mycotoxins, and Melasma: An Emerging, Still-Developing Picture

Mycotoxins can drive oxidative stress and inflammation at the cellular level. A 2021 study in the journal Toxins demonstrated that aflatoxin, a common mycotoxin, triggers oxidative stress and inflammatory gene activity in macrophages (a type of immune cell). A separate 2021 review in the International Journal of Molecular Sciences described how mycotoxins can damage epithelial barriers, activate inflammatory pathways (including the inflammasome), and disrupt gut microbial balance in ways that contribute to chronic, low-grade inflammatory states throughout the body — while its authors also candidly noted that the precise mechanisms linking mycotoxin exposure to disease progression in already-vulnerable individuals remain incompletely understood.

Why this matters for pigmentation: chronic inflammation and oxidative stress are not bystanders in melasma — they’re active participants in the same pathogenic processes discussed earlier, including melanocyte activation and the broader tissue crosstalk (with keratinocytes, blood vessels, and inflammatory mediators) that current research describes as central to melasma.

If mold-related illness sustains a background state of inflammation and oxidative stress, it’s biologically plausible that this could contribute to the same melanocyte-activating environment as UV exposure or hormonal shifts — but this is an inference from separate bodies of research, not something a study has directly tested in melasma patients.

Why This Matters for Treatment

Standard melasma treatment — sunscreen, tinted mineral SPF, topical lightening agents (like hydroquinone, azelaic acid, or tranexamic acid), sometimes procedures like chemical peels or lasers — works by targeting pigment after it’s already been produced, or by calming melanocyte activity locally. That’s valuable and often necessary. But for melasma that keeps returning despite excellent adherence to topical care, or that never fully lightens, it’s worth asking what’s continuing to activate melanocytes from the inside: Is cortisol chronically elevated from unmanaged stress? Is there undiagnosed or under-treated thyroid dysfunction, especially autoimmune thyroid disease? Is there an ongoing inflammatory load from an environmental exposure like mold that hasn’t been identified?

Practical Takeaways

• Continue foundational sun protection: broad-spectrum, tinted (iron-oxide-containing) sunscreen reapplied consistently — this remains non-negotiable regardless of root cause.
• If melasma appeared or worsened during a period of significant stress, consider that chronic cortisol elevation may be a contributing factor, and address stress physiology (sleep, nervous system regulation, mental health support) as part of your plan, not an afterthought.
• Ask your practitioner about thyroid function and thyroid antibody testing (TSH, free T4, anti-TPO, antithyroglobulin antibodies), particularly if melasma appeared alongside pregnancy, hormonal contraceptive use, or other symptoms suggestive of thyroid dysfunction (fatigue, hair thinning, temperature sensitivity, unexplained weight changes).
• If you have a known or suspected history of mold/water-damage exposure and unexplained chronic inflammatory symptoms, mention this to a practitioner experienced in environmental health as part of a broader workup — not as a stand-alone explanation for your melasma.
• Treat melasma management as a long game combining topical/procedural dermatologic care with root-cause investigation, not either/or.

 Bottom Line

Melasma is multifactorial, and several underlying factors may contribute to its development or persistence. Thyroid health, chronic stress and cortisol, and environmental exposures such as mold may all be worth considering, particularly when melasma persists despite standard treatment. The strength of evidence varies, and the potential connection between mold exposure and melasma still needs further research.

These factors don’t replace sun protection or dermatologic care, but they may provide additional areas to explore when looking beyond the skin alone.

If you’re navigating melasma, our 1:1 coaching program can help you better understand your symptoms and assess your health through comprehensive lab testing and a personalized, root-cause approach. Together, we can identify opportunities to optimize hormone and thyroid function, replenish nutrient stores, and provide your body with the support it needs to recover and thrive postpartum. Apply to work with us today!

References

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Lauren Papanos, MS, RD, CSSD, is a nationally recognized Registered Dietitian Nutritionist, board-certified sports dietitian, published researcher, and founder of Functional Fueling Nutrition®, an award winning endocrinology nutrition practice specializing in thyroid health, metabolism, fertility, and hormones. For more than a decade, she has helped thousands of active women uncover the physiological drivers behind hypothyroidism, chronic inflammation, fatigue and infertility through advanced laboratory testing and evidence-based nutrition. Lauren is the creator of the Energy Leaks framework, host of the Functional Fueling® Podcast, and author of The Thyroid Breakthrough, a guide that helps women understand why they can still struggle with thyroid symptoms despite eating well, exercising consistently, and having “normal” lab results.