Final answer:
An ingrown hair is a hair that curves back or grows sideways under the skin instead of emerging through the hair follicle. This can lead to discomfort and sometimes infection. The condition is a result of the obstruction of the hair follicle or sharp-edged hairs growing back improperly after being cut.
Step-by-step explanation:
A hair that grows through or follows an abnormal channel to the surface of the skin is commonly known as an ingrown hair. When a hair does not exit the hair follicle correctly and instead curves back or grows sideways under the skin, it is termed as ingrown. This can lead to irritation, redness, and sometimes infection.
The growth of hair begins deep within the hair follicle located in the dermis. Hair growth occurs when new cells form at the base of the hair, called the hair bulb. Older cells are pushed upward, becoming the hair shaft, which is primarily composed of dead, keratinized cells. This process is continuous, with the hair growing longer as the cycle proceeds.
However, when a hair follicle becomes obstructed or when hairs are cut and start to grow back with a sharper edge, they may not emerge straight through the skin. This can also happen due to improper shaving techniques or friction from tight clothing. In these cases, the hair may grow sideways or curl back under the skin, resulting in an ingrown hair.