Human hair and scalp oil, sebum, has a pH balance of between 4.5 and 5.5. This natural hair acidity prevents fungi and bacteria in the hair and scalp, and keeps the cuticle closed and healthy. When you then introduce alkaline hair products or a chemical that is more alkaline, the cuticles on your scalp may then open up, which leaves you at risk to hair loss, dullness, weakness and thinning.
You need to find out whether your hair is more alkaline or acidic. If you have an itchy, dry and flaky scalp, this would suggest that your hair has become more alkaline. While your scalp and hair are in this alkaline state, the natural sebum production will be off, making it unable to protect your scalp from infection, disease and hair loss. If you have permanently dyed or Bleached or relaxed hair, your hair was treated with a highly alkali substance to expose and change the hair’s cuticle.
If you have curly hair, then your cuticle is already partially open. It is especially important for people with curly hair to return their hair to a slightly acidic pH level. straight hair, due to the way the hair grows, the natural acidic sebum will be able to move through the hair easily, creating a pH balance that will keep the hair health.

How To Restore pH Balance Of Hair
Wash your hair with pH balanced shampoos and conditioners.
Use a natural acid to bring your hair into an acidic pH range, if your hair is naturally oily.
Simply mix together a tablespoon or two of apple cider vinegar (or even lemon juice) with 250ml of warm water. Pour through the hair and over the scalp, leave for a couple of minutes and rinse out with cool water.
You can pour aloe vera juice in a bottle and mist it over your hair