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Lip balms or salves constitute a special category of protecting and soothing cosmetics. They are intended to be applied to the lip pseudo-mucosa to relieve the signs and symptoms of skin dryness and chapping. Their function and formulation are described here.
Lips are usually submitted to an alternating sequence of wetting and drying from the tongue and accompanying saliva. Therefore, the osmotic stress of the skin cells in the lips is continuous. This organ also is frequently in contact with foreign materials such as food, drinks and toothpastes—as well as nonresident bacteria and yeasts from kissing. It is also continuously stretched and compressed.
Lip structure is not homogeneous, progressively changing from the conformational situation near its external border, similar to normal skin, to the organization near the oral cavity, similar to the mucosa epithelium. Lip skin does not possess sweat glands. Its lower layers are permeated by blood flow and nerve endings, making lips sensitive to temperature, pressure changes and abrasion. Like other skin, lip skin is subjected to changes associated with aging. UV radiation tends to contact the lower lip more, as a perpendicular surface, which makes photoaging worse in that area.
Skin sagging due to the progressive collapse of intercellular matrix polymers induces a deepening of the folds at the two corners of the mouth, with increased possibility for microbial growth. Smoking habits induce hardening of the lips and parallel wrinkling lines that are perpendicular to the lip borders. This presents a challenge to lip care application; if the fluid percentage in a lip care product is high, the product often diffuses inside lip wrinkles or outside of the lips due to capillary forces.
This is only an excerpt of the full article that appeared in Cosmetics & Toiletries, but you can purchase the full-text version.