👉Excess exposure to the sun.

Since melanin is released to absorb the sun’s rays, it is only logical that excess exposure to those rays will lead to an overproduction of melanin, resulting in dark spots on the skin and face.

👉Underlying medical condition.

The imbalance in melanin production may be because of an underlying condition such as Addison’s disease or other metabolic disorders. It could also be due to a physiological condition such as pregnancy.

👉Friction, injury, and damage.

If you notice increased hyperpigmentation after switching products, it is likely because your new products are too harsh on your skin. Your skin is producing more melanin than usual to protect itself from damage. It could also be a result of acne. It is common for acne to leave dark spots after treatment.

Dark inner thighs are also a consequence of friction from thighs rubbing together when walking. Often, this friction causes the sensitive skin to tear, leading to injuries that leave the area darker even after they heal.

👉Drugs and diet.

Yes, your diet definitely has an effect on your skin. Stay away from oily foods and switch to a healthier diet. Improvement in skin tone will be seen within weeks. Also, drugs that increase your sensitivity to light are known to cause darkening of the skin. A common example is birth control pills. Consider other alternatives of contraception if skin darkening is noticed. Other brands of oral contraceptives may be employed.

👉Having dark skin.

It is quite ironic that people with dark skin are more likely to have dark spots than other people. Though not much can be done about this, it is worth looking into ways to prevent or correct dark patches without damaging healthy skin cells.

Sources - guardian.org