Know the cycle · Hair-growth science
The four stages of the hair-growth cycle
Hair does not grow continuously or all at once. Individual follicles move through a repeating cycle commonly described as anagen, catagen, telogen and exogen.
01 / The cycle
Four phases, different roles.
At any one time, different hairs can be at different points in their cycle. Understanding those phases provides useful context for why light-based hair reduction is approached as a repeated routine rather than a one-off event.
Anagen
Active growth
The follicle is actively producing and growing the hair shaft.
Illustrative light pulse · general IPL principle
Catagen
Transition
Hair growth stops as the follicle enters a short regression phase.
Telogen
Rest
The follicle rests and the existing hair is no longer actively growing.
Exogen
Shedding
The existing hair is released and shed as the cycle continues.
02 / Phase by phase
Anagen — active growth
Anagen is the active-growth phase. During this stage, the follicle produces the hair shaft. Light-based hair reduction is associated with active growth, which is one reason treatment is repeated across the hair cycle.
Catagen — transition
Catagen is a short transition, or regression, phase in which active growth stops.
Telogen — rest
Telogen is a resting phase in which the existing hair is no longer actively growing.
Exogen — shedding
Exogen describes the release and shedding of the existing hair. Some scientific sources treat exogen as part of telogen rather than a completely separate phase, which is why CYPH/1 describes the four-stage model as one that is commonly used.
03 / Why it matters for IPL
A repeated routine, not phase detection.
IPL treatment does not identify the growth phase of an individual hair. Different hairs can be at different points in the cycle, so light-based hair reduction is repeated over time to allow treatment to coincide with hairs entering active growth.
04 / Sources
Evidence behind this article.
This article is general hair-cycle and IPL education. It does not make performance, safety or suitability claims about a future CYPH/1 product.
Cycle. Phase. One.
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