Hair loss, often used interchangeably with alopecia, develops when there are more hairs being lost as compared to the number of hairs regrowing. A large portion of a person's scalp hair is continually growing. This growth cycle lasts approximately four years. At any given time, about one tenth of the scalp hair stops growing and then is lost. Hair loss of approximately 50 to 100 hairs a day is considered normal. Normally when hair is lost, new hair begins growing again from the same hair follicle as previous. When this process is interrupted, there are likely other factors at play that a dermatologist can help you investigate.

Types of alopecia:

• Areata - a common form of alopecia that presents as small patches of hair loss usually around the size of a quarter that can develop anywhere on the scalp, face, or body. This may advance into either alopecia totalis or alopecia universalis but most commonly it remains patchy
• Ophiasis - a unique pattern of hair loss, which includes the sides and lower back of the scalp (called the occipital region) in the shape of a band or wave
• Totalis - a more advance form of alopecia that results in the complete loss of hair on the scalp
• Universalis - a rare and advanced form of alopecia which results in hair loss across the entire scalp and face (including eyebrows and eyelashes), plus the rest of the body (including pubic hair)
• Traction - caused by the hair being pulled in the same way for a long time, traction alopecia can happen to anyone who wears their hair pulled back tightly, whether in braids, dreadlocks, or a ponytail and can even occur when tight headwear is used in the same way every day.
• Androgenic - also known as male or female pattern hair loss, typically occurs on the top and front of the head for men while thinning occurs on the top and crown of the head for women. Although these patterns differ in men and women, they share the same genetic and hormonal roots

Other forms of hair loss:

• Telogen effluvium - a common form of temporary hair loss that usually happens after a person experiences severe stress, a shock, or a traumatic event such as surgery, childbirth, or serious illness
• Folliculitis decalvans - is characterised by redness, swelling, and pustules around the hair follicle that leads to destruction of the follicle and consequent permanent hair loss
• Autoimmune disorders - some autoimmune diseases, such as lupus, can cause hair loss as a result of immune cells attacking hair follicles or interfering with hair growth due to inflammation disrupting normal follicle function
• Nutrient and metabolic deficiencies - lack of certain dietary elements, such as protein and iron, or endocrine abnormalities like a thyroid disorder can negatively impact the hair growth cycle leading to brittle and thinning hair
• Drug induced hair loss - Many medications such as those used for birth control and for a variety of ailments including high blood pressure, heart disease, arthritis, and cancer may cause temporary hair loss which is usually reversible once the offending medication is stopped
• Chemically induced hair loss - Treating and processing hair with various styling chemicals that are too strong, or used too frequently, can result in weakened, fragile hair that is more prone to breakage and loss but is generally reversible when such treatments are stopped

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