The plant dye Henna imparts orange-red colour to skin and hairs due to its reaction with which of the following ?

Henna, derived from the plant Lawsonia inermis, contains a natural dye molecule known as lawsone (2-hydroxy-1,4-naphthoquinone) [t1, t7]. This molecule is responsible for the characteristic orange-red stain it leaves on skin and hair. The staining process occurs because lawsone has a high affinity for keratin, a fibrous structural protein found in the epidermis and hair shafts [t1, t5]. Mechanistically, lawsone molecules penetrate the tissue and form stable covalent bonds with the amino acids of the keratin proteins [t2, t5]. This chemical binding, often referred to as a Michael addition reaction, ensures the color is long-lasting and resistant to simple washing, as the pigment becomes an integral part of the protein structure [t1, t2]. Consequently, the reaction specifically involves proteins and their constituent amino acids rather than lipids, carbohydrates, or nucleic acids.