Are dark spots after pimples caused by melanin deposition?

In general, post-inflammatory pigmentation (dark spots left by pimples) is not entirely equivalent to melanin deposition, although melanin deposition is one of the primary causes of such pigmentation.

After acne subsides, localized capillary expansion or proliferation in the skin has not yet fully returned to its normal state, causing the skin to appear red. Red acne marks are mainly related to vascular dilation and inflammatory responses, rather than caused by melanin deposition. During the inflammatory process of acne, the skin is stimulated, causing melanocytes to become active and produce excessive melanin, which deposits in the epidermis or dermis, forming dark brown acne marks. This represents a typical type of acne mark caused by melanin deposition.

When the skin is subjected to inflammatory stimulation, melanocytes secrete more melanin to protect the skin from further damage. These melanin deposits within the skin cause acne marks to appear dark brown. Different individuals' skin reacts differently to inflammation, and there is also variation in the activity levels of melanocytes. Therefore, some people tend to develop dark brown acne marks after acne subsides, while others are less prone to this condition.

There are various methods for treating acne marks, including using products containing ingredients such as vitamin C and fruit acids to help fade melanin; phototherapy and laser treatments can promote collagen regeneration and improve skin texture; physical treatments such as microneedling and chemical peels can also help accelerate the fading of acne marks.