The darkening of the underarms of pregnant women is more common in clinical practice and may be related to fluctuations in hormone levels, excessive friction and genetic factors. 1. Hormone level fluctuations: after pregnancy, pregnant women will usually be affected by fluctuations in the level of estrogen and progesterone in the body, which will cause an increase in melanin-promoting cells, which will lead to hyperpigmentation in the armpit or pubic hair, manifesting itself as the darkening of the armpits. 2. Excessive friction: some pregnant women may be due to prolonged friction, thus stimulating the underarm area to appear hyperpigmentation. 3. Genetic factors: some pregnant women with dark armpits are considered to be genetically related, so pay attention to keep the armpits locally clean. For the phenomenon of pregnant women with dark armpits, if not accompanied by other symptoms, generally do not need special treatment, good hygiene care.