1. 黄褐斑 chloasma melasma

2. Definiton Melasma (also known as Chloasma faciei, or the mask of pregnancy when present in pregnant women) is a tan or dark skin discoloration. Although it can affect anyone, melasma is particularly common in women, especially pregnant women and those who are taking oral or patch contraceptives or hormone replacement therapy (HRT) medications.pregnant women

3. Causes Melasma is thought to be the stimulation of melanocytes by the female sex hormones estrogen and progesterone to produce more melanin pigments when the skin is exposed to sun. Women with a light brown skin type who are living in regions with intense sun exposure are particularly susceptible to developing this condition.melanocytesestrogenprogesteronemelanin Genetic predisposition is also a major factor in determining whether someone will develop melasma. The incidence of melasma also increases in patients with thyroid disease. thyroid disease It is thought that the overproduction of melanocyte-stimulating hormone (MSH) brought on by stress can cause outbreaks of this condition.melanocyte-stimulating hormone Other rare causes of melasma include allergic reaction to medications and cosmetics.

4. 临床表现 The symptoms of melasma are dark, irregular well demarcated hyperpigmented macules to patches commonly found on the upper cheek, nose, lips, upper lip, and forehead. These patches often develop gradually over time. Melasma does not cause any other symptoms beyond the cosmetic discoloration. Melasma is also common in pre-menopausal women. It is thought to be enhanced by surges in certain hormones.

7. Diagnosis Melasma is usually diagnosed visually or with assistance of a Wood's lamp (340 - 400 nm wavelength). Under Wood's lamp, excess melanin in the epidermis can be distinguished from that of the dermis.Wood's lamp melanin

8. Treatment The discoloration usually disappears spontaneously over a period of several months after giving birth or stopping the oral contraceptives or hormone replacement therapy. Treatments are often ineffective as it comes back with continued exposure to the sun. Treatments to hasten the fading of the discolored patches include:

9. Topical depigmenting agents, such as hydroquinone (HQ) either in over-the- counter (2%) or prescription (4%) strength. HQ is a chemical that inhibits tyrosinase, an enzyme involved in the production of melanin.hydroquinonemelanin TretinoinTretinoin, an acid that increases skin cell (keratinocyte) turnover. This treatment cannot be used during pregnancy.acid

10. Azelaic acidAzelaic acid (20%), thought to decrease the activity of melanocytes. Chemical peelsChemical peels. Microdermabrasion to dermabrasion (light to deep). Galvanic or ultrasound facials with a combination of a topical crème/gel. Either in an aesthetician's office or as a home massager unit. Laser and IPL Oral Tranexamic acid has shown to provide rapid and sustained lightening in melasma by decreasing melanogenesis in epidermal melanocytes

11. In all of these treatments the effects are gradual and a strict avoidance of sunlight is required. The use of broad-spectrum sunscreens with physical blockers, such as titanium dioxide and zinc dioxide is preferred over that with only chemical blockers. This is because UV-A, UV-B and visible lights are all capable of stimulating pigment production.pigment Patients should avoid other precipitants including hormonal triggers. Cosmetic camouflageCosmetic camouflage can also be used to hide melasma.