Hair is much more complicated than it looks, and it serves multiple purposes. It protects the skin from dust and dirt, helps regulate body temperature, traps particles that may cause infections, and can even help us express ourselves through our hairstyles. And while many of us take it for granted, there’s a lot that goes into making our locks grow strong and healthy.
Each hair grows from a tiny, saclike hole in the skin called a hair follicle. Inside the follicle is a cluster of special cells that reproduce to make more hair. As the cells multiply, they start to push up through the skin until they hit a saclike structure at the bottom of the hair follicle called the hair bulb. This structure is supplied with blood by a blood vessel called the hair papilla. The papilla is surrounded by nerves that sense when hair moves or gets pulled.
Once the cell clusters reach the hair bulb, they stop reproducing and instead start to produce hard proteins called keratin. The keratin is insoluble in water, so it forms a waterproof coating that protects the rest of the hair from damage. The keratin also helps give hair its color, texture, and strength. The first layer of the hair shaft is a thin, protective sheath called the cuticle. This sheath consists of flattened, overlapping cuticle cells that are coated with a hydrophobic lipid layer. It is this outer surface that gives hair its smooth appearance and enables it to reflect light.
The next layer of the hair shaft is the cortex. This is where all the hair’s color and texture come from. It’s also where the hair’s strength comes from. The cortical layer is made up of closely packed spindle-shaped cells filled with keratin filaments. The last layer of the hair shaft is a central medulla that’s found in thicker hair. The medulla is a soft, spongy mass of tissue that’s responsible for some of the hair’s flexibility and resilience.
All of these layers are held together by a cellular membrane complex that consists mainly of lipid mono- and bilayers. This complex reflects light in a pattern that’s characteristic of a lamellar periodicity with rings at spacings about 4.3 A. The ring-like appearance is also visible in 2-dimensional X-ray scattering data.
There are several things that can affect how your hair grows and behaves, including genetics, hormones (such as estrogen), stress, diet, and nutrition. For example, if you’re deficient in certain nutrients, your hair could become thinner or more brittle. Hormone levels also change during different stages of life, which can lead to slower or faster hair growth.
Hair is very complicated and there are countless variations of color, texture, and length. For instance, medium hair is the most common type and is not as fragile as fine or coarse hair. However, it can still be damaged by over-styling with heat tools and improper techniques, says Hill. The key to strengthening this type of hair is taking a dual approach that includes both protecting the cuticle and addressing the cortex with a rich, protein-rich conditioner.