Whatever form of hair loss TE takes, it is fully reversible. The hair follicles are not permanently or irreversibly affected; there are just more hair follicles in a resting state than there should normally be.
There are three basic ways TE can develop.
1. There might be an environmental insult that "shocks" the growing hair follicles so much that they decide to go into a resting state for a while. This results in an increase in hair shedding and a diffuse thinning of hair on the scalp. This form of TE can develop rapidly and may be noticeable one or two months after receiving the shock. If the trigger is short lived, then the hair follicles will return to their growing state and start producing new hair fibers pretty quickly. This form of TE usually lasts less than six months and the affected individual has a normal scalp hair density again within a year.
2. The second form of TE develops more slowly and persists longer. The hair follicles may not all suddenly shed their hair fibers and enter a resting telogen state. Rather, the follicles may enter a resting state as they normally would, but instead of returning to a new anagen hair growing state after a month or two, they stay in their telogen state for a prolonged period of time.
This results in a gradual accumulation of hair follicles in a telogen state and progressively fewer and fewer anagen hair follicles are left growing hair. In this form of TE, there may not be much noticeable hair shedding, but there will be a slow thinning of the scalp hair. This form of TE is more likely to occur in response to a persistent trigger factor.
3. In a third type of TE, the hair follicles do not stay in a resting state but rather cycle through truncated growth cycles. When this happens, the individual experiences thin scalp hair and persistent shedding of short, thin hair fibers.
Causes of Telogen Effluvium: Stress and Diet
What are the trigger factors for TE? The short answer is many and varied. Classic short-term TE often happens to women soon after giving birth. Called postpartum alopecia, the sudden change in hormone levels at birth is such a shock to the hair follicles that they shut down for a while. There may be some significant hair shedding, but most women regrow their hair quickly.