How hair grows has a lot more in common with your garden than just terminology. Read on to find out more…
In the beginning…
Hair growth begins deep inside the hair follicle and yet the only part of the hair defined as alive is at the very bottom of the follicle. It is called the bulb.
The bulb, or hair root, contains the living cells that grow the hair while the visible part of the hair, the shaft, is considered dead. Other important structures in the hair follicle include the sebaceous gland which produces oil to lubricate the hair, the arrector pili muscle which, when activated, will cause the hair to stand up (goose bumps), and the bulge.
Most importantly, the bulge is where the cells are stored to regenerate the bulb when it is lost at the end of each growth cycle. It is the bulge which needs to be targeted by any successful form of permanent hair removal.All images on this page can be enlarged. Click on or touch the image.
Hair ColoursAll natural hair colours are the result of just 2 types of hair pigments and both of these are derivatives of melanin.
Eumelanin is the dominant pigment in brown and black hair, while pheomelanin is dominant in red hair. Blond hair is actually the result of having little pigmentation at all in the hair strand while grey and white hair occur when melanin production stops.
Hair thickness is simply determined by follicle size and not colour or curliness. An individual’s hair volume, as a result, can be thin, normal, or thick from the same number of hairs of any colour.
Curly HairThe shape of the hair shaft has a direct effect on the curliness of your hair. A very round shaft resists movement with the same pressure in every direction encouraging it to remain straight.
The flatter or more elliptical the hair shaft becomes the curlier hair gets. Because the shape favours bending in one direction, the hair soon begins to curl after leaving the follicle.
Hair TypesHair grows everywhere on the body except on mucus membranes and what is called glabrous skin. Glabrous skin occurs in areas such as the palms of the hands, soles of the feet, and lips. As a new-born, we have all our hair follicles, but they are populated by just one hair type: vellus hair.
Vellus hair is a fine, slow growing and almost transparent hair often simply called peach fuzz. The thicker, pigmented, faster-growing hair is called terminal hair. Over time, growth and sex hormones influence how hair grows causing hair follicles to switch production from vellus to terminal hair in the typical male and female hair growth patterns.
Hair Growth CycleHair follows a growth cycle with three distinct phases: anagen, catagen, and telogen. Importantly, all 3 occur simultaneously across the skin with each strand of hair on the body at its own phase of development. While one strand of hair may be in the anagen phase, another may be in the telogen phase.
The overall effect is for the volume of hair to appear constant despite some follicles being dormant (no hair) and others just beginning to grow new hair. The average rate of growth for hair is 1.25cm per month or 15cm per year.
Hair length is determined more by the length of the Anagen (growing) phase than by the speed of hair growth. Scalp hair has the longest growth stage and is therefore capable of growing the longest hair while eyelashes and eyebrows have the fastest growth rate yet remain much shorter because of their brief growing phase.
Hair Growth StagesAnagen Phase
The anagen phase is commonly known as the growth phase. This is the phase where the hair grows approximately 1cm per month. Hair on the scalp can grow for 2 – 6 years in anagen phase. At the other extreme, eyebrows will grow for just 4 – 8 weeks. The longer the hair stays in the anagen phase, the longer it will grow.
The catagen phase is also known as the transitional phase. During this time, which lasts about 2 weeks, the bulb detaches and “rests”. While remaining in the follicle, the hair strand is cut off from its nourishing blood supply and stops growing.
During the telogen, or resting phase, the follicle remains dormant for 1 – 4 months. Around 10% – 15% of scalp hair is in this phase of growth at any given time. Now the follicle lining is all that temporarily anchors the hair in place. Eventually the hair will work its way free and the hair will be shed. Within weeks, a new hair shaft will begin to emerge and the cycle begins again.
Significance of the Bulge
The search for stem cells
Hairs regenerate and follicles undergo significant changes throughout the hair cycle and this has always suggested the presence of stem cells. At first it was believed that stem cells were likely to be located near the bulb or root of the hair.
Instead, they were eventually discovered in the bulge located alongside the arrector pili muscle more than half way up the follicle. This explained the well-known observation of the follicle retracting back up to the erector pipi muscle during early anagen stage. It is now understood that this is the mechanism by which stem cells migrate to the base of the follicle and re-establish a bulb in order to grow new hair.
Why Laser and Thermolysis are not effective
This also gave the answer to why Galvanic Electrolysis is so effective at permanent hair removal.
In galvanic electrolysis, a small electric current is passed through a thin metal probe into the hair follicle. This converts moisture in the follicle into sodium hydroxide which is able to completely destroy the contents and lining of the follicle. Most importantly, it removes the bulge and its stem cells responsible for new hair production. The probe is then removed along with the hair and the follicle contents. This is how electrolysis achieves permanent hair removal.
In contrast, Thermolysis (known as single needle electrolysis) and Laser remove existing visible hair, but only permanently destroy 1 in 10 hairs at each treatment. This allows the remainder to eventually regrow and for this reason Laser and Thermolysis are only permitted to describe themselves as “permanent hair reduction” in the USA. These poor results from Laser are because the bulge and it’s stem cells are relatively transparent and therefore immune to heating by laser light. The bulge is also not in contact with the hair itself and remains immune to the heat produced by Thermolysis.
The exception to this is during early anagen stage when the hair root is raised to be adjacent to the bulge. During this brief time, the bulge is well connected to the hair root and heat in the root is transmitted to the bulge with the ability to damage or destroy it. This robs the follicle of it’s ability to grow another hair.