Causes of thinning hair

Age

Hair follicles reduce in the rate which they replenish with the course of age and this is a completely normal process. This is in alignment with the rest the human body – where age affects the ability for the body to regenerate itself.

Can cause:
 Age-related Alopecia

Diet & lifestyle

With age the body becomes less and less able to utilise protein consumed via diet - which in turn affects the rejuvenation of hair as protein is an essential nutrient supporting hair follicles.

Can cause:
 Age-related Alopecia

The progression of Androgenic Alopecia is also believed to be influenced by a poor diet which can affect new hair growth as well as an inactive lifestyle which can reduce hair producing androgen (hormone) levels.

Can cause:
 Androgenic Alopecia

In addition, Telogen Effluvium can be significantly brought on by changes in diet like crash dieting, anorexia, and low protein intake as the hair is not receiving essential nutrients.

Can cause:
 Telogen Effluvium

Auto-immune disease

The immune system makes white blood cells (lymphocytes) and antibodies to attack bacteria, viruses, and other 'germs'. If you have an auto-immune disease, your immune system 'mistakes' parts of your body as foreign and can mistake hair roots (hair follicles) as 'foreign'. This causes mild inflammation leading hairs to become 'weak' and fall out.
Auto-immune disease is also often passed down through family.

Can cause:
 Alopecia Areata

Thyroid dysfunction

An over active or under active thyroid gland can often lead to thinning hair due to changes in hormone levels. Research conducted by the University of British Columbia found a strong relation between people with Alopecia Areata also having thyroid disease.

Can cause:
 Alopecia Areata

Polycystic Ovary Syndrome (PCOS)

Polycystic ovary syndrome (PCOS) affects approximately 5% of all women and is the most common hormonal disorder among women of reproductive age. Women with PCOS can experience loss hair due to a hormone imbalance and increased sensitivity to male hormones such as testosterone. A male hormone called dihydrotestosterone (DHT), which is converted from testosterone, binds to sites on hair follicles and appears to make the follicles go into their "resting" phase sooner, which in turn starts to cause the hairs produced by those follicles to become thinner and thinner with each growth cycle.

Can cause:
 Androgenic Alopecia

Hereditary

Hair loss can be genetically passed from either the mother or the father via a gene called the AR or the androgenic receptor. Androgens are hormones (such as testosterone) that stimulate hair growth when they bind with androgen receptors (AR).
Studies suggest that some genes determine a disjointed relationship between the AR and androgens which can lead to an increased risk of patterned thinning hair in men and women.

Can cause:
 Androgenic Alopecia

Illness & Stress

Temporary thinning hair can be caused by illness such as iron-deficiency/anaemia, severe infection, major surgery and periods of psychological stress in an individual’s life. When an individual experiences stress or illness, chemicals in the body transmit signals to the hair follicles, causing them to enter the resting phase. During this phase there is no new hair growth.

Can cause:
 Telogen Effluvium

In addition, it is also believed that psychological stress and extreme shock can significantly trigger auto-immune disease of the hair follicles, leading hairs to become 'weak' and fall out.

Can cause:
 Alopecia Areata

When we are stressed, we can also often eat badly which prevents our bodies from getting the vital nutrients needed to support the hair follicles. See Diet & lifestyle

Post birth

The rise in progesterone hormones during pregnancy keeps hair growing for longer. But after delivery, the progesterone hormones return to normal levels, causing the hair that should have fallen out during the last nine months to do so all at once. This thinning hair tends to peak between three and four months after delivery as the hair follicles rejuvenate themselves but is temporary with hair growth returning to normal within six to 12 months.

Can cause:
 Telogen Effluvium

Menopause

Hormonal changes brought on by pre-menopause and menopause can also lead to thinning hair. During this time estrogens and progesterone levels in a woman's body fluctuate and decrease. These changes can affect the function of the hair follicle resulting in extended resting phases and notable hair thinning.

Can cause:
 Telogen Effluvium

Medication

eMedicine (the online evidence-based medical reference) states that medications can significantly bring on Telogen Effluvium, of which the most frequently cited are beta-blockers, anticoagulants, retinoids (including excess vitamin A), propylthiouracil (induces hypothyroidism), carbamazepine, and immunisations

Can cause:
 Telogen Effluvium

In addition, drugs used to treat cancer can shut down the hair follicle making the hair fall out.

Can cause:
 Anagen Effluvium

Overstyling

Traction Alopecia is caused by tight ponytail-hairstyles, use of strong colouring chemicals, over-tight braids and hair extensions. The condition is often temporary and once the 'traction' element has been removed, normal growth often returns. However, in some cases it can be permanent.

Can cause:
 Traction Alopecia