A brief overview of chemical damage to hair weathering

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Severely Weathered Hair (Trichorrhexis nodosa)
The term “weathered hair” means severe damage or breakage in the hair shaft structure which is generally caused by various chemical and physical treatments done to the hair fiber such as the excess use of curling, bleaching or the improper use of other hair straightening products.

In a normal scalp every hair fiber or shaft undergoes minor cuticular and secondary cortical breakdown at the tip before being shed at the end of the hair growth cycle. A moderate amount of breakage in the hair fiber is absolutely normal which can be due to any reason like harsh combing or tight braiding. But in weathered hair vigorous breakage occurs from the middle of the hair fiber. The damage in weathered hair occurs mainly due to the stripping off of the cuticle layer.

The function of the cuticle layer is to encase the cortex in a strong protective layer. It provides physical support and protects the cortex from environmental factors such as ultra violet rays, chemicals such as detergents and physical action such as hair brushing. If the cuticle is absent then the cortex underneath is exposed.

The cortex is less resistant to the physical and chemical damage to hair when compared to the cuticle layer. The chemical bonds, present in the cortex, which provide strength to the hair, are broken down when exposed leaving the hair weaker and divided into minute frays. The weak hair is very brittle and prone to breakage.

Trichorrhexis nodosa- the most severe form of hair weathering
One of the most common hair shaft defects a dermatologist encounters of cuticle destruction is trichorrhexis nodosa (also called trichonodosis). Trichorrhexis nodosa is a focal 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 which are known as nodes. It is because of these characteristic appearance of nodes that the disease is called trichorrhexis nodosa.

The point of cuticle breakdown leads to the formation of several minute frays which is the characteristic feature of severely weathered hair.


There can be many reasons for stripping of the cuticle layer - . It can be either genetic or metabolic such as in those conditions that involve abnormal urea synthesis, abnormal copper or zinc metabolism, or defective cysteine or sulfur incorporation into hair fiber (trichothiodystrophy).

Some people have naturally weak hair where the cuticle layer is not properly produced. This can be an hereditary trait that runs commonly in families. Congenital trichorrhexis nodosa due to hereditary causes is very rare and it first develops at a very young age. Sometimes the cuticle layer is not healthy due to metabolic disorders such as abnormal urea synthesis, abnormal copper or zinc metabolism etc.

Yet, the most common cause of hair weathering in Trichorrhexis nodosa is acquired, caused due excessive use of treatments on hair or due to excessive manipulation of the hair. Too much brushing, complex and tight hairstyles, excessive cleansing, dying, and perming may disrupt the cuticle cells. These harsh treatments disturb the structure of a healthy hair shaft. Trichorrhexis nodosa is seen in people who repeatedly use hot combs or permanent waves to style their hair.

As already described, hair shafts that are affected by trichorhexis nodosa contain small nodes at irregular intervals throughout the length of the shaft. The number of nodes may vary from one to several, depending on the length of the hair. Multiple nodes indicate severe disruption on the cuticle layer and more exposure to the underlying cortical fibers to separate and fray easily.

The cortical fibers splay outwards and fracture, giving an appearance of brooms to the hair strand. Depending upon the appearance the disease can be mainly divide into 2 types.

Types of Trichorrhexis nodosa

Trichorrhexis nodosa that occurs due to the excess use of cosmetics can be of two types:
  • Proximal trichorrhexis nodosa
  • Distal trichorrhexis nodosa
  • Proximal trichorrhexis nodosa is common in black African-Americans due to the high use caustic chemicals like relaxers and permanent waving. As their hair is tightly coiled the formation of nodes and breakage of hair occurs quite close to the skin of the scalp.
  • Distal trichorrhexis nodosa primarily occurs in Caucasian or Asian individuals who have straight hair. Nodes and breakage of the hair strand occur several inches away from the scalp resulting in dull and uneven hair.
Treatment of Trichorrhexis nodosa

The only treatment for this severe form of acquired weathering is to stop the use of hard hair brushes and avoid hair styling that involves chemicals. Once the protective layer of the hair fiber is broken down there is little that can be done to repair it. Often, it is recommended to choose a short hair style and cut off the defective hair, though it may take some time for the hair to recover from trichorrhexis nodosa.

So it is better not to let the hair become weathered as once damaged it may take several months or even years to recover completely.

Rodney Dawber, “Hair: Its Structure and Response to Cosmetic Preparations”, 1996; Clinics in Dermatology, 14:105-112
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