Telogen Defluvium is nothing other than Androgenetic Defluvium (pattern hair loss).
With Telogen Defluvium the number of hairs lost does not exceed 100. With the pull test only two or three hairs at most are usually obtained. This means that due to the defluvium, the anagen phase has become temporally shorter (compared to its usually length), thus reducing the ability of hair follicles to sustain hair growth.
An alteration of the trichogram is almost non-existent with a number of hair in the anagen phase at around 80% due to a temporal reduction of the anagen phase of the hair follicle.

Due to a very short anagen phase, between 10% and 60% of fallen hair are short, thin and with bulbs that have a very thin diameter. They are moreover located on the surface of the dermis compared to hair that has a normal growth cycle. This hair is in between terminal hair and vellus hair.
It is included among hair in the involution phase with a short anagen phase and therefore is considered like hair in the premature telogen phase which falls out before its time. It is short and thin because it does not have time to develop (short anagen phase), it appears small and involute after a very short anagen phase and is characteristic of this form of hair loss. The follicle remains histologically present for a long time, even if it is not as deep and contains a hair that is increasingly involute. Only very late does this hair go towards hyalinosis.

This is a pathological process that may manifest in various bodily structures, characterized by the intra- and extra-cellular accumulation of material, called hyaliane, which damages the structure and function of the affected areas, resulting in progressive atrophy. The hair loss resulting from this is similar to a scarring form with loss of the skin adnexa.
We can distinguish between an acute form of Telogen Defluvium (very intense and characterized by a temporary loss of hair) and a chronic form of Telogen Defluvium (a modest type with a constant loss of hair).
In men common causes of Telogen Defluvium are both pattern hair loss (chronic telogen defluvium) and male frontoparietal alopecia (chronic telogen defluvium).
Instead, in women common causes of Telogen Defluvium are more numerous. Among them we note: pattern hair loss from drugs (acute telogen defluvium), post-menopause hair loss (acute telogen defluvium), hair loss from androgen secreting tumors (acute telogen defluvium), hereditary hair loss (chronic telogen defluvium), polycystic ovary hair loss, congenital adrenal hyperplasia hair loss (acute telogen defluvium), hair loss from anorexia nervosa (acute telogen defluvium) and lastly hair loss from hyperprolactinemia (acute telogen defluvium).