Estrogen is the primary hormone behind melasma, but progesterone plays a significant supporting role. Both hormones directly stimulate the skin cells that produce pigment, which is why melasma so often appears during pregnancy, while taking birth control pills, or during hormone replacement therapy. The relationship between hormones and melasma is more complex than a single trigger, though, involving multiple forms of estrogen, vascular changes in the skin, and even thyroid function.
How Estrogen Drives Pigment Production
Your skin contains pigment-producing cells called melanocytes, and these cells have estrogen receptors on their surface. When estrogen binds to those receptors, it switches on the genes responsible for producing melanin, the pigment that gives skin its color. Specifically, estrogen ramps up the activity of the key enzymes melanocytes use to manufacture melanin. It also triggers rapid chemical signals inside the cell that promote both melanin production and melanocyte proliferation, meaning the body is making more pigment and more pigment-producing cells at the same time.
There are actually three forms of estrogen in the body, and each contributes differently. Estradiol (the most potent form) directly activates melanin-producing enzymes through gene signaling. Estrone, a weaker form, works through a slightly different pathway but achieves the same result: it boosts the master regulator of melanocyte development and function. Estriol, the form that surges during pregnancy, influences oxidative stress pathways in skin cells, which can indirectly push melanin production higher.
Beyond pigment itself, estrogen promotes the growth of new blood vessels in affected skin. This increased vascularity is now recognized as a core feature of melasma patches, not just a side effect. Researchers have identified estrogen and blood vessel growth as two of the most significant factors in the condition, which is why newer treatment approaches aim to target both simultaneously.
Progesterone’s Role
Progesterone independently stimulates melanin production through its own set of receptors. When it binds to those receptors, it activates a signaling chain that ultimately turns on the same pigment-producing enzymes estrogen targets. But progesterone adds a second mechanism: it increases oxidative stress within skin cells by raising markers of cellular damage while simultaneously lowering the skin’s natural antioxidant defenses. This disrupted balance further stimulates melanin synthesis.
Progesterone also boosts blood vessel growth in the skin by increasing production of a growth factor called VEGF, which leads to greater vascular density and inflammatory cell activity in melasma patches. This means progesterone doesn’t just darken the skin directly; it reshapes the local skin environment in ways that sustain and intensify pigmentation. A progesterone byproduct called 20α-DHP may contribute as well, activating the same master signaling axis that controls melanocyte behavior.
Why Pregnancy Is a Major Trigger
Pregnancy is one of the most common times melasma appears, and the timing lines up precisely with hormone levels. Lesions typically show up during the second or third trimester, when estrogen and progesterone reach their peak concentrations. Both hormones are elevated many times above their normal levels during this window, creating ideal conditions for melanocyte overstimulation.
The good news is that pregnancy-related melasma often fades on its own. It typically regresses within a year after delivery as hormone levels return to baseline. The less encouraging reality: up to 30% of cases persist even after 10 years, suggesting that once the pigment pathways are activated, they can become self-sustaining in some people regardless of hormone levels.
Birth Control Pills and Hormone Therapy
Oral contraceptives are among the strongest drug-related triggers for melasma. In a large pharmacovigilance analysis of FDA adverse event reports, contraception accounted for 27% of all drug indications linked to melasma cases. Combination pills containing ethinylestradiol paired with various progestins showed the strongest associations, with ethinylestradiol and norethindrone topping the list. This makes sense given that these pills deliver both estrogen and a synthetic progesterone, hitting both hormonal pathways at once.
In certain populations, melasma prevalence can reach as high as 50%, and hormonal contraceptive use is a well-established contributor to those numbers. If you developed melasma after starting a new birth control pill, the hormonal connection is likely direct. Switching to a non-hormonal contraceptive method may help, though existing pigmentation can take months to fade even after the hormonal stimulus is removed.
Thyroid Hormones and Melasma
The hormonal picture extends beyond sex hormones. Thyroid dysfunction appears in melasma patients at surprisingly high rates. One study found thyroid disorders in 58.3% of melasma patients, a rate four times higher than in controls. Among women who developed melasma during pregnancy or while on oral contraceptives, 70% had thyroid abnormalities. Another study found thyroid disorders in 37.8% of melasma patients compared to 11.1% of healthy controls, with hypothyroidism and thyroid autoimmunity being the most common findings.
The exact mechanism connecting thyroid hormones to skin pigmentation isn’t fully mapped, but researchers have identified that the melanocortin system (the signaling network that controls melanocyte activity) interacts with the thyroid hormone axis. Thyroid hormones also stimulate production of inflammatory signaling molecules, and elevated levels of these molecules are found in people with thyroid overactivity. This inflammatory environment may prime melanocytes to overproduce pigment. If you have melasma, particularly if it appeared without an obvious hormonal trigger like pregnancy or birth control, thyroid screening may be worth discussing.
Melasma in Men
Though melasma overwhelmingly affects women, men get it too, and the hormonal story flips. A case-control study in Indonesia found that men with melasma had dramatically lower testosterone levels than men without it: an average of 7.55 nmol/L compared to 21.07 nmol/L in controls. Men with testosterone levels at or below 8.92 nmol/L had nearly seven times the risk of developing melasma.
The correlation was striking. Higher melasma severity scores corresponded almost perfectly with lower testosterone, showing a strong negative correlation. At normal levels, testosterone appears to suppress the chemical activity that drives melanin production. When testosterone drops, that brake is released, and pigment-producing enzymes become overactive. So while elevated estrogen and progesterone trigger melasma in women, it’s the absence of adequate testosterone that creates vulnerability in men.
UV Light Amplifies the Hormonal Effect
Hormones alone don’t fully explain melasma. Ultraviolet light is the essential co-factor. Sun exposure stimulates melanocytes independently of hormones, and when both signals converge on the same cells, the result is far more intense than either trigger alone. This is why melasma worsens in summer, appears primarily on sun-exposed areas of the face, and resists treatment in people who don’t adopt rigorous sun protection.
The interplay works in both directions. UV exposure can alter hormone receptor expression in skin, potentially making melanocytes more sensitive to circulating estrogen and progesterone. Meanwhile, the vascular changes that estrogen and progesterone create in melasma patches may deliver more blood flow and inflammatory signals to the area, amplifying the skin’s response to UV damage. This feedback loop is a major reason melasma is so persistent.
How Hormonal Melasma Is Managed
Because hormones are a root driver, managing melasma means addressing both the pigment that’s already there and the ongoing hormonal stimulation. An international expert consensus identifies broad-spectrum sunscreen as the single most essential step, since blocking UV removes the co-factor that hormones need to trigger visible darkening. Without consistent sun protection, no other treatment works well.
For active treatment, a triple combination cream containing a skin-lightening agent, a mild steroid, and a retinoid remains the gold standard. Alternatives include topical azelaic acid and kojic acid. Oral tranexamic acid, which works by interrupting the signaling between UV-damaged skin cells and melanocytes, has gained recognition as an effective option. Chemical peels and microneedling can boost the effectiveness of topical treatments, while laser therapy is generally reserved for cases that don’t respond to other approaches.
If your melasma is tied to a hormonal source you can modify, such as oral contraceptives, removing that trigger gives other treatments a better chance of working. For triggers you can’t change, like pregnancy or natural hormonal fluctuations, consistent sun protection combined with topical treatment offers the most reliable path to improvement. Recurrence is common because the underlying hormonal sensitivity doesn’t disappear, which makes long-term maintenance a realistic expectation rather than a one-time fix.