Later in life the genetic material can be changed by epigenetic modifications, i.e. chemical alterations of the DNA the affect the activity of the genes. (sciencedaily.com)
This condition is thought to be caused by chemical alterations in the nervous system that can occur during old age. (dummies.com)
Dog foods that are labelled «natural» mean that all ingredients are in their natural forms and have not undergone scary chemical alterations. (dogfoodking.com)