There may be several of the periods of growth and rest before the hair reaches its full length and is ready to drop out. Then. if a rest period arrives in time and the hair is not combed or pulled out, it may cling to the skin until the new growth pushes it out. The follicle has a tendency to contract about the old hair and help to hold it in. Hair grows faster by day than by night, and faster in the warmer summer months than in the colder winter months. Hair is dead, and the rate of growth of a new hair is twice as fast as it is near the end of the hair's life.
Hair begins to grow before birth.
That is, the germs of the future hairs appear on the forehead and eyebrows in the tenth or twelfth week of the human embryo. Two weeks later the germs show above the lips, and in the sixteenth week on the rest of your head. After that the trunk, limbs and backs of the hands and feet show the hair germ. These are merely short, peg-like protuberances on the outer skin of the embryo. Active growth of hair on the scalp begins immediately after it appears.