On the depth of penetration of fruit acid
Fruit acid is used for skin maintenance, and the study of its penetration depth is quite critical.

Among fruit acids, glycolic acid is common. Skin structure, from the outside to the inside, there are stratum corneum, granular layer, spinous layer, basal layer, etc. The stratum corneum is the first barrier of the skin, composed of multiple layers of flat keratinocytes.

The molecule of glycolic acid is small and has a certain hydrophilicity. At the beginning of its penetration, it mostly acts on the stratum corneum. By virtue of its own characteristics, glycolic acid can loosen the connection between the keratinocytes, causing the stratum corneum to gradually fall off and thin. In this process, it may be shallow into the granular layer.

However, the cells in the granular layer are closely arranged, and there are lipid-rich lamellar corpuscles, which hinder the further penetration of glycolic acid. Therefore, under normal circumstances, it is difficult for glycolic acid to penetrate the granular layer significantly, and it is more rare to penetrate deep into the spinous layer and the basal layer.

To make glycolic acid penetrate deeper, many factors need to be considered. First, the level of concentration. Moderately increasing the concentration of glycolic acid can indeed enhance its permeability. However, if the concentration is too high, although it may increase the depth of penetration, it will greatly increase the risk of skin irritation, which is easy to cause skin redness, swelling, tingling and other discomfort. Second, the effect time is long. Prolonging the contact time between glycolic acid and the skin is theoretically beneficial to penetration, but it should be moderate, otherwise it will also cause damage to the skin. Third, the state of the skin. Dry skin, oily skin and sensitive skin have different reactions and tolerances to glycolic acid. Dry skin has a thinner stratum corneum, and glycolic acid may penetrate relatively easily, but it is also more vulnerable to damage; oily skin has a thicker stratum corneum, and glycolic acid penetration may be slightly more difficult; sensitive skin is more sensitive to glycolic acid stimulation.

Overall, the penetration depth of glycolic acid is mostly limited to the stratum corneum and the shallow layer of granules. To precisely control its penetration depth, it is necessary to weigh many factors such as concentration, time and skin condition in order to achieve the effect of skin care and avoid the risk of skin damage.