Henna, a natural plant dye, produces an orange-red stain on skin and hair by interacting primarily with which of the following substances?

Explanation

Henna's characteristic orange-red coloration on skin and hair results from its chemical reaction with proteins and amino acids present in the keratin of hair and skin cells. This interaction forms a stable dye complex, whereas lipids, carbohydrates, or free amino acids alone do not produce this staining effect.