Proteins and hair

Key takeaways

• Hydrolysed proteins can measurably raise the breaking force of damaged hair in the lab. In a 2016 ex vivo test (Daniels et al.) on bleached, permed and heat-damaged tresses, hydrolysed keratin (600 Da, 0.5%) improved wet tensile strength on all three damage types. Hydrolysed wheat protein (1,500 Da, 2%) was best for dry hair, especially bleached or heat-treated, and hydrolysed collagen (9,000 Da, 2%) gave the most consistent gain on heat-damaged hair. It was a small, industry-style study with one hair source.
• Smaller is not automatically better, and it is not one dial. The effects depended on the protein, the damage type and wet versus dry testing.
• Hydrolysed keratin forms a film and partly enters the cortex. A Unilever-co-authored study found it deposited on the cuticle, partly penetrated, and that treated hair kept its tensile strength after UV exposure while untreated hair lost 14.32%. Fan 2025
• The "protein-moisture balance" idea (too much protein makes hair stiff and brittle, too little moisture makes it mushy) is community folk theory. We found no controlled study testing it and none defining "protein overload" in hair. It may still be a useful way to describe how a product feels.
• Hair cannot "absorb" protein to replace what it lost. Proteins and peptides deposit on or partly in the fibre and wash out over time. They do not rebuild the keratin structure (see bond builders).
• Allergy risk is real but small. Hydrolysed protein conditioners have caused contact urticaria, mostly in people with atopic dermatitis. A 1998 Finnish study found 12 reactors to a hydrolysed collagen conditioner ingredient, all women with atopic dermatitis. Niinimaki 1998 The Cosmetic Ingredient Review panel judges hydrolysed wheat protein safe when the average molecular weight is 3,500 Da or less. Burnett 2018

The science

Hair is about 90% keratin protein. Damage from bleach, heat, perms, sun and friction loses protein, oxidises cystine and roughens the cuticle. Cosmetic proteins are hydrolysates, short peptide fragments from wool or feather keratin, wheat, silk, rice, soy or collagen, often given a positive charge so they stick to negatively charged damaged hair. Their proposed benefits are film formation (smoothness, gloss), filling gaps, hydrogen bonding in the outer fibre and extra stiffness on drying. In the tensile experiment, the authors proposed that wheat's strength gain in dry hair partly reflects wheat starch stiffening as it dries.

Evidence is limited to cut hair and mostly small, industry-linked studies. A feather-keratin hydrolysate study found better hydration with heat, deposits at the cuticle edges and a smoother look under the microscope, but no tensile or on-head outcome. Villa 2013

What it means for your hair

• Bleached, relaxed or heat-damaged (high-porosity) hair is the most plausible target.
• Low-porosity, virgin or fine hair has little to gain, and very high levels may feel stiff (anecdotal).
• With atopic dermatitis or wheat allergy, be careful with wheat or collagen hydrolysates and patch test.

Myths and facts

• Myth: if hair feels mushy it needs protein, and if it feels stiff it needs moisture. Untested.
• Myth: protein "fills holes" permanently. It rinses out.
• Fact: different hydrolysed proteins do different things on different damage, and there is no best one.

Bottom line

For bleached or heat-damaged hair, a hydrolysed keratin or wheat conditioner is a reasonable, cheap choice. Expect smoothness and some breakage reduction, not repair. Do not stack many protein products, since there is no evidence either way, and avoid wheat or collagen hydrolysates if you have had hives from hair products.

Ingredient pages: hydrolysed keratin, wheat protein, silk, rice protein, amino acids, ceramides, 18-MEA.