Hair is categorized in various ways, so the question of “how many types of hair are there” does not have one straightforward answer. Hair is a filamentous structure composed primarily of keratinized protein, but classification shifts based on its biological function, physical shape, or ability to manage moisture. The main ways to classify hair involve examining its fundamental biological purpose, its visible texture and shape, and its internal characteristic of porosity.
The Two Fundamental Biological Types
The human body develops two distinct biological types of hair, which are differentiated by their structure, location, and role in the body. These two forms are vellus hair and terminal hair, and they represent the primary scientific classification system.
Vellus hair is the fine, short, light-colored hair often referred to as “peach fuzz” that covers most of the body. Its primary function is to provide insulation, aiding in the regulation of body temperature. Structurally, vellus hair is typically non-pigmented and lacks a medulla, the central core found in thicker hair shafts.
Terminal hair, by contrast, is longer, thicker, and more deeply pigmented, growing from follicles that extend deeper into the skin. This type of hair makes up the eyebrows, eyelashes, and the hair on the scalp, developing in areas like the armpits and pubic region after puberty due to hormonal influences. Terminal hair helps protect the body, such as shielding the scalp from the sun’s rays, and it has a longer active growth phase compared to vellus hair. The transition from fine vellus hair to coarse terminal hair is often triggered by androgens, a type of sex hormone.
Classifying Hair by Shape and Texture
The most common system for categorizing hair is based on its visible shape and texture. This classification is genetically determined by the shape of the hair follicle; a perfectly round follicle produces straight hair, while an increasingly oval or flat follicle produces wavy, curly, or coily hair. The system divides hair into four main types (Type 1 to Type 4), with each further broken down into sub-categories (A, B, C) based on the width or tightness of the pattern.
Type 1 hair is straight and typically lies flat on the scalp, allowing natural oils to travel down the shaft easily, which can sometimes make it prone to greasiness. Sub-types range from 1A, which is fine and bone-straight, to 1C, which is thicker and may have a slight, resistant wave.
Type 2 hair is wavy, forming an “S” shape that is generally looser than a curl. Sub-types range from 2A, which is fine and easily styled, to 2C, which has more defined waves that start closer to the root and are more prone to frizz.
Type 3 hair is curly, characterized by clear spirals or ringlets that tend to be voluminous. Type 3A curls are loose and large, while 3C curls are tight, corkscrew-shaped coils that are often densely packed. As the curl pattern tightens, the hair becomes more susceptible to dryness because the coiled shape makes it difficult for scalp oils to travel the full length of the strand.
Type 4 hair is coily or kinky, featuring the tightest curl patterns, ranging from tightly defined coils (4A) to a very dense zigzag pattern (4B). The 4C sub-type is the most tightly coiled, often having an almost invisible curl pattern. This texture gives it high density but requires intensive moisture care to prevent breakage. This system is widely used to guide hair care routines, as different shapes require different levels of moisture and manipulation.
Classification Based on Porosity
Beyond visible texture, hair porosity describes the hair shaft’s ability to absorb and retain moisture. Porosity is determined by the state of the cuticle, the hair’s outermost layer, which acts like shingles on a roof. The condition of these cuticles dictates how easily water and products can pass into the hair’s cortex.
Low porosity hair has tightly bound, flat cuticles that resist the absorption of moisture, often causing products to sit on the surface rather than penetrating the shaft. While this hair type retains moisture well once it is inside, it can be difficult to saturate when washing and often takes a long time to air dry. To help products absorb, this type of hair benefits from gentle heat, such as during deep conditioning treatments, to slightly lift the cuticle.
Medium porosity hair has a looser cuticle structure that allows for a balanced exchange of moisture, meaning it absorbs and retains hydration effectively. This balance makes medium porosity hair easy to manage, style, and less prone to damage, as the cuticles are just slightly raised.
High porosity hair has raised, widely spaced, or damaged cuticles, meaning moisture is quickly absorbed but also quickly lost. This rapid loss can lead to chronic dryness, frizz, and brittleness, especially when damage is caused by chemical processing, excessive heat, or environmental factors. For high porosity hair, care focuses on using sealing products and heavy butters to lock in the moisture.