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Causes of hair loss

Occasional and chronic hair loss or androgenetic alopecia can affect anyone, both men and women. The causes are numerous and can be difficult to identify. Here's an overview.

What does a hair’s life cycle look like?

To fully understand the process of hair loss and its cause, you must consider the pattern of hair growth. The hair’s growth is cyclical in nature and is characterized by phases of regression and regeneration. Each cycle is comprised of three main phases:
  • The anagen phase is associated with hair growth. During this phase, the matrix cells of the bulb multiply. The hair shaft is produced by the hair follicle during this phase. This phase, during which hair grows one centimeter per month, lasts on average two to six years. 
  • The catagen phase is a transition phase during which the hair follicle becomes inactive. The hair stops growing for two to three weeks. The regression of the hair follicle places the dermal papilla closer to the stem cells in the bulb. 
  • The telogen phase, during which no production of the hair shaft is observed, lasts two to three months. The “dead” hairs, pushed out by new hairs in the anagen phase, fall out. On a daily basis, you lose 25 to 60 hairs, which you are apt to find on your brush or clothing.
Under normal conditions, each hair follicle follows its own cycle. This prevents the different hair cycle phases from occurring simultaneously on all the hair follicles. Therefore, a normal scalp contains approximately 100,000 hairs, 86% of which are in anagen phase*.

Hair loss in women: commonly caused by hormones

It can be difficult to pinpoint the exact cause of hair loss, especially when it is temporary. Nonetheless, hormonal changes are among the first factors taken into consideration by specialists. It has been scientifically observed and established that hormones are involved at some level, to a greater or lesser extent, in the various types of hair loss: acute telogen effluvium (occasional hair loss), chronic telogen effluvium (chronic hair loss), androgenetic alopecia and hair aging.
The vast majority of patients seeking consultation for hair loss are women. In women, hair loss caused by hormonal changes is fairly common:
  • It is not uncommon to observe a link between oral contraceptives and hair loss. The cause: the composition and dose of hormones which can vary from one oral contraceptive to the next. For example, progestin-only contraceptives can have androgenetic effects on the hair which could lead to occasional diffuse hair loss. Progestins combined with estrogens can, on the other hand, have a positive effect on hair quality. 
  • Also, the hormonal fluctuations observed during the postpartum period often result in occasional hair loss. The cause: the drop in estrogen levels after a pregnancy. Specialists estimate that one-third, or even one-half, of women will experience hair loss following a pregnancy**. 
  • Thyroid disorders are often cited as the cause of chronic telogen effluvium (the scientific term for chronic hair loss, developing sporadically over a period of more than six months). It often appears in individuals with healthy hair initially. The same causes can trigger this type of hair loss in men as well.
  • The mechanism by which androgenetic alopecia manifests is also hormonal and involves the androgen receptors found in the dermal papilla. This chronic diffuse hair loss (lasting a period of more than six months) usually appears between the ages of 30 and 40 years. Over their lifetime, 70% to 80% of men are affected, versus 29% to 42% of women. In a number of cases, alopecia is hereditary, and is caused by the same factors when it affects women. 

But the cause of alopecia is not always hormonal...

Hair loss in younger women can have other, non-hormonal causes. 
  • Stress-related hair loss involves a particular physiological mechanism: when the cells in the scalp are exposed to sudden or intense stress, they release neurotransmitters (substance P) that trigger an acute inflammatory cascade. The latter inhibits the normal hair cycle: the hair enters the telogen phase prematurely, resulting in sudden hair loss three to four months after the triggering factor. This is reactional hair loss or acute telogen effluvium. 
  • There is a strong link between fatigue and hair loss. Physical and psychological fatigue can contribute to several types of hair loss: 
  1. either occasional hair loss following a triggering factor linked to, for example, a stressful situation
  2. or chronic hair loss linked, for example, to anemia, caused by an iron deficiency. Closely linked to fatigue, hair loss associated with a dietary deficiency can cause sporadic hair loss lasting more than six months. 
  • Traction alopecia is regarded as a mechanical, rather than physiological, hair loss. Due to overly tight or heavy hairstyles, for example, the hair follicle is impacted directly. By pulling on the scalp, the hair fiber moves further and further away from its cavity. Repeated pulling on the hair can cause alopecia by the age of 30, and sometimes even younger.
  • Medication-induced alopecia refers to reactional hair loss that is associated with certain treatments. The major drug classes to monitor are: anticoagulants, antidepressants, anticonvulsants, antihypertensive medications, certain anti-inflammatories, thyroid treatments, beta-blockers, certain anti-cholesterol treatments, medications containing lithium and retinoids. 
The administration of chemotherapy cancer treatments or exposure of the head and neck to radiation therapy are also responsible for a specific type of hair loss. 

* Source: Olsen, 1994; Shapiro, 1996
** Source: Grover and Khurana, 2013
*** Source: Blume-Peytavi et al., 2011; Wang et al., 2010

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My anti-occasional female hair loss routine (less than 6 months)

Action against occasional hair loss (caused by stress, fatigue, post-pregnancy, changing seasons, etc.)

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My anti-chronic female hair loss routine (over 6 months)

Action against chronic hair loss

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Action against chronic hair loss (> 6 months)

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