When a medical condition causes hair loss in patches, it's referred to as alopecia areatahttp://www.health24.com/Medical/Diseases/Alopecia-Areata-Client-20120721.
This chronic inflammatory condition occurs when your body’s immune system attacks hair follicles – structures that contain the roots of the hair – resulting in distinct areas of hair loss (also called patchy hair loss).
Read: Causes of hair loss
Not all hair loss is the same in everyone - some can experience simple thinning of their hair while others lose all the hair on their head and even body.
Hair loss can be gradual or it can happen suddenly.
And it can happen to anyone, young and old, male and female, and children too.
It's also normal for women between the ages of 40 and 50 to lose about 20 percent of their hair.
Before you panic at that brush full of hair, remember that we all lose between 70 and 100 hairs a day from the scalp, and only when we've lost about 50% of them does the loss become noticeable.
Interestingly, hair also grows faster in the summer, during sleep and between the ages of 16 and 25. Studies have also shown that women, especially, lose more hair in summer and less in winter.
The three phases of the hair growth life cycle:
Anagen or growth phase
Catogen or intermediate phaseTelogen or resting phase
90% of scalp hairs are growing and 10% are resting at any one time.
Even though it’s not contagious or life-threatening, hair loss can often be a great source of distress, resulting in low self-esteem and depression.
There are many types of hair loss, each with a different cause.
Seasonality of hair shedding in healthy women complaining of hair loss, Dermatology, 2009.
Environmental Factors Affecting Hair Loss in Desert Climates, Evans, D.J. & H.A.
American Academy of Dermatology