Glycolic acid is a type of alpha-hydroxy acid (AHA) derived from sugar cane and is a commonly used ingredient in skincare products, including serums, due to its exfoliating properties. It works by dissolving the bonds between dead skin cells on the surface of the skin, allowing them to be sloughed away more easily. This process of exfoliation can help to reduce the appearance of dark spots.

Dark spots, also known as hyperpigmentation, occur when an excess of melanin, the brown pigment that produces normal skin color, forms deposits in the skin. This can be caused by sun damage, inflammation, acne, hormonal changes, or aging.

Glycolic acid can help to reduce the appearance of these dark spots in several ways. Firstly, by speeding up cell turnover, it can help to remove the layers of pigmented cells, revealing fresher, less pigmented skin underneath. Secondly, glycolic acid can also help to inhibit the enzyme tyrosinase, which is involved in the production of melanin. By doing so, it can help to prevent the formation of new dark spots.

However, it's important to note that while glycolic acid can be effective, it's also a potent ingredient that can cause irritation, especially for those with sensitive skin. It's always recommended to start with a lower concentration and gradually build up, and to always use sun protection, as AHAs can make your skin more sensitive to the sun.

Lastly, while glycolic acid can help to reduce the appearance of dark spots, it's not a quick fix. It can take several weeks or even months of consistent use to see noticeable results. For more stubborn dark spots, other treatments such as laser therapy or prescription creams may be more effective.