To understand how UV rays can cause hair damage it is important to understand hair chemistry.
The cuticle is the outermost part of our hair; it is composed of proteins and covalently bonded lipids. When these bonds are broken, the cortex, which lays underneath the cuticle becomes exposed making the hair more susceptible to damage.
Environmental UV rays from the sun can degrade these lipid layers found in the cuticle exposing the cortex and putting your hair on the fast track to damage, split ends and fading of color treated hair.
The cortex consists of keratin filaments, which are held together by disulphide and hydrogen bonds. These disulphide bonds are what becomes broken when we color, perm or relax our hair.
Once that first line of defense has been compromised UVA and UVB rays break down the bonds that comprise the dye molecules in colour just like they break down the hair’s natural melanin. Creating those natural highlights you see when you spend time outdoors in the sun, this is another reason why the hair is always lighter on the ends compared to the roots.
Hair that is gray, fine or highly porous (from natural texture, or chemical processing), can experience more of a dramatic colour shift and general damage from the sun.
How to protect your hair from sun damage:
Preventative is the best course of action. Since the hair is not living once it is damaged it cannot be repaired.
Cover up, where a sun hat.
Reinforce the protective lipid layer with a good conditioner, hair oil and deep conditioning treatments.