What could be the cause of an oval-shaped light brown patch under the armpit?

Nov 28, 2025 Source: Cainiu Health

Dr. Liu Wenmin

Introduction

In general, oval-shaped light brown patches under the armpits may be caused by friction-induced pigmentation, hormonal changes, tinea versicolor, café-au-lait spots, seborrheic keratosis, or other reasons. It is recommended to seek medical attention promptly, identify the underlying cause, and receive appropriate treatment under a doctor's guidance. In daily life, keep the armpit area clean and dry, and avoid frequent use of irritating bath products.

Generally, oval light brown patches under the armpits may be caused by friction-induced pigmentation, hormonal changes, pityriasis versicolor, café-au-lait spots, seborrheic keratosis, and other reasons. It is recommended to seek medical attention promptly, identify the underlying cause, and receive appropriate treatment under a doctor's guidance. Specific analyses are as follows:

1. Friction-induced pigmentation: Long-term wearing of tight clothing causes repeated friction on the skin under the armpits, leading to local accumulation of melanin and formation of pigmented spots. Switching to loose, breathable cotton clothing can reduce friction. After daily cleansing with lukewarm water, apply vitamin E cream to promote melanin metabolism.

2. Hormonal changes: During pregnancy, puberty, or endocrine disorders, fluctuations in hormone levels stimulate melanocytes, resulting in pigmentation. Maintaining regular sleep patterns and avoiding staying up late may allow some pigmented spots to fade naturally once hormone levels stabilize. Daily sun protection for the underarm area is also recommended.

3. Pityriasis versicolor: A fungal infection affecting the skin under the armpits, presenting as round, light brown patches accompanied by mild scaling. Patients should follow medical advice to apply topical antifungal agents such as ketoconazole cream, miconazole and clobetasol cream, or terbinafine hydrochloride cream. Frequent clothing changes and sun exposure for disinfection are also important.

4. Café-au-lait spot: A congenital pigmented lesion that may appear as a round, light brown patch under the armpit with well-defined borders. If cosmetically concerning, patients can seek medical treatment with Q-switched laser therapy, which uses laser energy to break down melanin particles. Multiple sessions may gradually lighten the pigmentation.

5. Seborrheic keratosis: Caused by skin aging leading to abnormal proliferation of keratinocytes, forming rough-surfaced, light brown patches. Under medical guidance, patients may use topical medications such as tretinoin cream, fluorouracil ointment, or salicylic acid ointment to soften keratin. Alternatively, cryotherapy can be performed, using low temperatures to destroy the affected tissue and remove the lesion.

In daily life, keep the underarm area clean and dry, and avoid frequent use of irritating bath products. Eat more fresh fruits and vegetables rich in vitamin C, such as oranges and strawberries, to help reduce melanin production. Avoid scratching or picking at the pigmented areas to prevent skin damage and potential infection.

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