Hair growth begins in the follicle and the average person should be able to grow about 4-7 inches1 a year regardless if it is straight or curly, healthy or unhealthy, coarse or fine. The follicle has several layers each designed to assist and protect the hair strand as it grows out of the skin. Each follicle is also connected to a sebaceous gland secreting sebum (an oily secretion) onto the surface of the skin. The oil from this gland is all our scalp requires to stay moisturised and does NOT need additional help. There is no need to grease your scalp, NO NEED!! (My poor head! All throughout my life I was always told to grease my scalp, my follicles were probably suffocating!). The base of the follicle is also known as the hair bulb and is found in the dermis (the second layer of your skin). Here the follicle obtains nourishment from the blood vessels and nerves in the dermal papilla – the commander of the scalp. The dermal papilla controls the scalp and organizes when, how quickly and how thickly your hair grows.
Hair growth occurs in three circular phases: anagen, catagen and telogen.
Anagen - the growth period - can last anywhere from 1-10 years2 (so the average head of hair can potentially grow 4-70 (!) inches in a given growth period) but the average length is about 3 years. During anagen, keratinocytes in the follicle produce keratin to make the hair shaft. As it is the longest period in the cycle the majority (90%) of your follicles are in the anagen phase right now.
The remaining 10% are in either the catagen phase (the transition period) or the telogen phase (the rest phase). Catagen lasts about three weeks2 and in this phase the hair is prevented from growing or producing melanin (which is why the bulb is white). The follicles shrink and the dermal papilla begins to break down in preparation for telogen. Telogen takes about three months, here the hair pretty much just waits there until stimulated to undergo exogen (shedding).
After about ten growth cycles our ability to pigment our hair worsens and we begin to develop grey hairs1 (this also happens during periods of stress, which is why during or after exams you may find random greys1), if you have a shorter growth cycle you also may discover yourself going grey earlier! More bad news: less than half of women and 2% (!!!!) of men go through life with a full head of hair3. So the lesson is, if you think your male friend going bald is hilarious right now there’s a 1 in 2 chance that’ll be you in the future (almost 100% if you’re a boy reading this)! :D
1 Krause, K; Foitzik, K (2006). Biology of the Hair Follicle: The Basics. Seminars in Cutaneous Medicine and Surgery, Volume 25, Issue 1.
2. Bernard A. Bruno (2003). Hair Shape of Curly Hair. Journal of the American Academy of Dermatology, Volume 48, S120-6
3. Lai-Cheong, J.E; McGrath, J.A (2009). Structure and Function of Skin, Hair and Nails. Medicine, Volume 37, Issue 5Images taken from The Medical Dictionary & Stylecraze
PS. Happy Independence Day to Ghana! xx