“Hair cycle implies sequential phases of growth and rest that each follicle goes through which includes anagen (active hair growth), catagen (involution) and telogen phase (resting). The anagen phase may last for about 2 to 8 years, the catagen phase lasts for 4 to 6 weeks and the telogen phase lasts for 2 to 3 months. The exogen phase of hair follicle (the release of telogen hair) coincides with the end of telogen phase. In the normal scalp, 90–95% of the hair follicles are in the anagen phase and the remainder (5–10%) in the telogen phase with about 100-150 hair being shed daily. Only a few follicles will be in the transitional or catagen phase. The biological clock that determines the end of the anagen phase and the beginning of the catagen/telogen phase is a complex phenomenon whose molecular basis is being unveiled. Various metabolic alterations such as pregnancy, malnutrition and other stressful conditions are capable of influencing the biological clock within hair follicles and it is possible for abnormally large number of hair follicles to enter the telogen phase simultaneously.” Malkud S.
Mnemonic is ACT. Each hair follicle goes through an ACT.
| Anagen phase (active hair growth) | E.g. Anabolic |
| Catagen phase (involution/degeneration of the hair) | E.g. Catabolic |
| Telogen phase (resting) | E.g. telo- means “end; at the end: complete; final “ |
Reference / Further Reading
Malkud S. Telogen Effluvium: A Review. Journal of Clinical and Diagnostic Research : JCDR. 2015;9(9):WE01-WE03. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4606321/