If your hair is protein-deficient, there are a few surefire tell-tale signs that you should watch out for. The first and most obvious is the lack of elasticity. If your hair is not springy enough and doesn’t return to shape once tugged at (instead, it breaks off or sits limply), then it is definitely protein deficient. Limp hair, hair which is prone to excessive frizz, breakage and porosity and so on, are also in need of a protein treatment. And lastly, if your hair has been recently coloured, you should make sure you nourish it with protein.