There are two types of protein; those derived from animal sources and those from plant sources.
Animal proteins are stronger/more potent than plant proteins. They coat the outer layers of the hair shaft while plant (vegetable) proteins are absorbed into the hair shaft.
Proteins are identified by the terms keratin, collagen, elastin or amino acid and of course the word protein.
Common proteins used in hair products are keratin, placenta, collagen, silk, wheat, corn, soy, oats. Other proteins used in homemade hair masks are; molasses, coconut milk, eggs, and yogurt.
The type and size of protein determine whether or not it can actually be absorbed by the hair.
Hydrolyzed proteins are proteins that have been broken down into amino acids which are said to easily penetrate the layers of the hair shaft. They are said to be the best type to use for strengthening hair.
Proteins like soy, wheat, collagen, keratin are too big to penetrate (they condition the hair).
Whole eggs/egg white/albumin/egg albumin, avocado, bananas and aloe vera are all sources of whole protein. They don’t behave in the same way as hydrolyzed protein, amino acids or peptides.
Some people with protein sensitive hair will find whole proteins to be perfectly fine to use.
Be aware of protein allergies.
Some people are allergic to hydrolyzed proteins in hair products. Application of these type of protein can lead to an itchy skin/rash (contact urticaria). Should a certain product causes your scalp to itch, avoid using it again and if you can, try to figure out which ingredient you are allergic to.