However, if the chemical processing is very severe, it alone can do so much damage to the hair fiber that the fiber at the root is severely weakened. If this happens, the hair may break off at the skin surface. The result is called a diffuse alopecia.
As well as chemically-induced damage, physical processes can also harm the hair. Aggressive brushing, back combing, and other grooming techniques that put a lot of physical stress on the hair fiber can cause the cuticle to flake and strip away.
Inappropriate use of a hair dryer can also cause a lot of damage. When you wash your hair, some water gets under the cuticle and into the cortex. If you dry your hair with a high heat you heat up the water. This makes the water expand inside the hair and this literally pushes outward to leave spaces in the hair fiber. In severe cases the hair develops little bubbles inside, a condition called "bubble hair." These bubbles make the hair much weaker and likely to break off. If damaging physical processes are combined with damaging chemical processes then the problem is compounded.
Physical damage to the hair through overprocessing is difficult to treat. The best approach is to cut off as much damaged hair as possible, avoid further chemical processing, be gentle with your hair, and wait for new, undamaged hair to grow in. While there are cosmetic treatments to help "glue" damaged hair back together, they only work for a short time and have to be reapplied regularly. The end result is never as good as the original, undamaged hair.
One of the most common hair shaft defects a dermatologist encounters is trichorrhexis nodosa (also called trichonodosis). Trichorrhexis nodosa is a defect in the hair fiber. When observed under the microscope most of a hair shaft looks entirely normal. However, in isolated spots along the length of a fiber swelling and/or fraying can be seen. These focal defects develop where there is an absence of cuticle.