Lanugo hair, commonly known as womb hair, begins to grow on the embryo about five months after conception. Lanugo hair is soft, fine, and generally very light. Prior to delivery, lanugo hairs are quickly replaced with vellus hairs, which is referred to as fuzz on newborn infants. Vellus hairs are present, on mature adults, on the forehead, ears, and even the scalp--particularly when adults lose their hair, due to balding.
Adults have three main kinds of hair; all three kinds are always in one of the three stages of growth. Terminal hairs, found on the limbs and trunk of the body, is dark and coarse, and grows at a slower rate than hair on the scalp. Eyebrows consist of primary terminal hair, while pubic hair is secondary terminal hair. Vellus hair is found on the forehead, ears, and even the scalp of mature adults who have begun to bald. Intermediate hair, commonly referred to as transitional hair, is in the process of shifting from terminal to vellus hair, or vice versa.
Phase 1 of hair growth consists of active growth, which lasts for years. Most of our hair is in the active growth phase, growing about half a millimeter per day. Hair grows much faster on women than on men. In this phase, the rate of hair growth and hair coloration both are affected by dihydrotestosterone (DHT); as DHT levels increase, the length of the hair growth phase grows shorter and individuals notice their hair becoming finer and thinner, with less color properties.
The catagen phase is a transition phase occurring at the end of the active growth cycle and signaling the end of the active growth of a hair. The catagen phase lasts for 2 to 3 weeks, and involves people losing 75 to 100 hairs from their scalp per day. In the catagen phase, hair shrinks to 1/6 its original diameter, the "root" is diminished, and the dermal papilla, which normally serves as a source of nutrition for a hair follicle, breaks away.
At any one time, 10 to 15 percent of the hairs on your body are in the resting phase. In the resting phase, which lasts for three months, hair is neither growing nor falling out. The dermal papilla is still broken away from the hair follicle. After the resting phase, hair strands begin to fall out, and are replaced with a new active phase. The dermal papilla and hair follicle reconnects, and new strands of hair dislodge the old strands.