Hair follicles are small, tube-like structures in the skin that produce hair. They are located all over the body and can be found in both thick and thin patches depending on heredity and hormonal influences. Each follicle contains a muscle and an oil gland, which helps to grow and nourish the hair. The cycle of growth consists of three phases: active phase (anagen), catagen, and telogen. During the anagen phase, new hair is formed, while in the catagen phase, the hair follicle transitions from growing to resting stage. In the telogen phase, the old hair falls out and a new one starts to grow.