There are many causes of hair loss. When there is loss of hair all over the scalp, and not just in patches, it is known as generalized or diffuse hair loss. This can be sudden in onset or can happen over long periods. The sudden onset of diffuse hair loss is called acute telogen effluvium. Common causes of acute telogen effluvium include Post viral fever hair loss, post-pregnancy hair loss, hair loss which follows fad diets, and hair loss after any severe illness or surgery. This hair loss is self-limiting and the hair regrows by itself.
Sometimes, hair loss does not stop but is persistent. This is called chronic telogen effluvium and is more common in women. This may be because of underlying problems like thyroid dysfunction, vitamin deficiency, anaemia or binge eating habits. In such patients, further evaluation with a blood test may be needed for these conditions to be diagnosed.
The male and female pattern hair loss may also start as diffuse hair loss before the patterns are established. These can be diagnosed by dermoscopy.