There are many different types of hair, including straight, curly, wavy, and coily. Depending on a person’s hair type, they may need to follow different care instructions. This article will provide some general information about hair types and detail some specific care instructions. Part 1 What does hair type mean? Share on PinterestInfographic by Diego Sabogal Hair type typically refers to the shape of a person’s hair. Hair can be straight, wavy, curly, or coily. According to one 2020 articleTrusted Source, hair consists of two structures: the strand of hair itself, or the hair shaft, and the hair follicle. The hair shaft consists of different layers, including the cortex, the surrounding cells, and, in thicker hair, a central medulla. A 2017 studyTrusted Source notes that the shape of the hair follicle determines the shape of a person’s hair. For example, the hair follicles for curly hair are in the shape of an S. Genetic factors play a role in deciding the shape of a person’s hair follicle. What types of hair are there? Hair shape refers to the degree of curliness of a person’s hair. One review articleTrusted Source notes that different researchers have used different hair shape categorization systems in their research about hair. For example, some have used use labels such as: • stick straight • straight • wavy • big curls • small curls Some hairstylists like to distinguish hair shapes into four categories. However, scientists do not use this categorization system in medicine or scientific research. Hairstylists use the following categorization system: Hair type Shape Type 1: Straight • 1a: Very straight, fine or thin texture • 1b: Straight with some bends • 1c: Straight with a coarser texture Type 2: Wavy • 2a: Wavy and fine • 2b: Wavy with a slightly more defined S-shape • 2c: Wavy with well-defined S-shaped waves Type 3: Curly • 3a: Loose curls • 3b: Tight and springy curls • 3c: An S or Z shape that springs back into shape when stretched Type 4: Coily • 4a: Loose coils • 4b: Zig-zagging coils • 4c: Tight coils Density Hair density refers to the number of hairs that a person has on their head. The more hairs a person has, the higher that person’s hair density. Hair structure Hair structure refers to the thickness of the strands of hair. A person’s hair can be: • fine • medium • coarse According to the World Trichology Society (WTS), hair thickness varies depending on the person. Some people have finer hairs than others. The WTS also notes that the hair fibers become shorter and finer as a person ages. Porosity Hair porosity is a measure of the amount of moisture that a person’s hair can absorb. Hair porosity depends on how many gaps or tears are present in the cuticle layer. The cuticle is the outer layer of the hair, which protects it from wear and tear. According to one 2015 articleTrusted Source, hair is naturally porous. However, hair that has sustained damaged due to bleaching or chemical treatments is more porous than untreated hair. People may find it helpful to avoid strong chemical and high heat treatments to let their hair recover.