Shedding hair is natural, and more hair is shed at certain times of the year. However, internal and external stressors can result in large fall out of hair which can lead to significant distress and concern. There seems to be a link between stress and how it changes hair follicle biochemistry.
Hair follicles on the scalp do not grow hair continuously. They cycle through an active growth stage for two or more years, then regress to a resting stage. This resting stage lasts up to two months before going into a fall out stage which is part of a new growth cycle. At any time on a healthy human scalp, 80-90% of the hair follicles are actively growing hair. That leaves 10-20% of scalp hair follicles in a resting or fall out state called Telogen.
When the body experiences a significant emotional or physical stressor – such as an accident, an operation, loss of a loved one, rapid weight loss, or hormonal changes – a larger percentage of hair remains in the fall out phase and widespread thinning of hair on the scalp occurs. Handfuls of hair are often noticed in the shower or on a comb within two months of the initial stress.
People with this type of hair loss, also referred to as Telogen Effluvium, never lose all their hair. Rather, their hair appears noticeably thin. While hair loss is often limited to the scalp, in more serious cases the hair loss can affect other areas, like the eyebrows or pubic area. This form of hair loss usually lasts less than six months and with no more stress, the affected individual’s hair will recover to its previous density within a year.
The good news is that in most cases, the hair loss is fully reversible once the stressor is eliminated. The hair follicles are not permanently affected; there were just more hair follicles in a resting state than there should normally be.
More persistent insults to the body, for example chronic emotional or nutritional stress, can lead to persistent hair thinning, also referred to as chronic Telogen Effluvium.