Afro-textured hair, or kinky hair, is a human hair texture originating from sub-Saharan Africa. Each strand of this hair type grows in a tiny, angle-like helix shape. The overall effect is such that, contrasted with straight, wavy, or curly hair, afro-textured hair appears denser. Terminology English adjectives such as "woolly", "kinky", "nappy", or "spiraled" have been used to describe natural afro-textured hair. More formally, ulotrichous ("curly-haired" from and ) refers to afro-textured hair, its antonym being leiotrichous ("smooth-haired"). Jean Baptiste Bory de Saint-Vincent in 1825 introduced the scientific term Oulotrichi for the purpose of human taxonomy. In 1997, hairstylist Andre Walker created a numerical grading system for human hair types. The Andre Walker Hair Typing System classifies afro-textured hair as 'type 4' (there are other types of hair, defined as type 1 for straight hair, type 2 for wavy, and type 3 for curly, with the letters A, B, and C used as indicators of the degree of coil variation in each type), with the subcategory of type 4C being most exemplary of the afro-textured hair. However, afro-textured hair is often difficult to categorize because of the many different variations among individuals. Those variations include pattern (mainly tight coils), pattern size (watch spring to chalk), density (sparse to dense), strand diameter (fine, medium, coarse), and feel (cottony, woolly, spongy). Different genetic groups have observable differences in the structure, density, and growth rate of hair. With regard to structure, all human hair has the same basic chemical composition in terms of keratin protein content. Franbourg et al. have found that black hair may differ in the distribution of lipids throughout the hair shaft. Classical afro-textured hair has been found to be not as densely concentrated on the scalp as other follicle types. Specifically, the average density of afro-textured hair was found to be approximately 190 hairs per square centimeter. This was significantly lower than that of European hair, which, on average, has approximately 227 hairs per square centimeter. Loussourarn found that afro-textured hair grows at an average rate of approximately 256 micrometers per day, whereas European-textured straight hair grows at approximately 396 micrometers per day. In addition, due to a phenomenon called 'shrinkage', kinky hair that is a given length when stretched straight can appear much shorter when allowed to naturally coil. Shrinkage is most evident when afro-textured hair is (or has recently been) wet. The more coiled the hair texture,