Our hair and nails are predominately made of protein, which gives them strength. Overtime we lose the needed protein to keep our hair and nails strong because our body doesn't store protein. The hair may experience breakage and excessive damage with the use of heating appliances, chemicals, and other harsh practices. In order to keep the hair strong, we must replenish the lost protein. This can be done internally, through eating a protein rich diet and externally by applying products that contain protein to the hair.
A protein rich diet isn't just great for your hair, but also for your body. Because our bodies' don't have a protein reservoir, it's important to eat protein rich foods regularly. Some really good sources of protein are almonds, avocados, bacon, baked beans, beef, broccoli, carrots, salmon, rice, soy bean, turkey and tuna. Eating these foods (and many other protein rich foods), can help to replenish the protein from the inside.
Replenishing protein externally will also aid in strengthening the hair. Hair care products may contain many different forms of protein, which may come from different sources and have different levels of potency. Most of them do the same thing; aid in strengthening the hair by filling in the weak or brittle areas of the strand; depending on the strength; the end results may differ greatly. Some proteins will soften the hair, some will aid in giving it a shiny coat, others may be really strong and may leave the hair dry; so you definitely want to read the labels and follow the instructions carefully.
Protein is most commonly replenished through a conditioning treatment; this is why many of them instruct you keep the conditioner on for a while or to use heat to further the effects; heat will open up the strands and allow the protein to be deposited. Many moisturizers also include protein in them, which you need to be careful of. Although protein is excellent to keep the hair strong, too much of this good thing can be extremely bad.
Protein overload is the term used when too much protein is applied to the hair, causing it to become dry and brittle. Many people purchase a shampoo, conditioner and daily moisturizer with protein in it in order to keep the hair strong, but this is too much and may lead to damage. Using a mild protein treatment once a week (or every other week at the minimum), is generally enough to keep the hair strong. Some people will use a potent treatment every 6-8 weeks to boost the protein levels, but these are generally extremely drying to the hair; the hair has to be handled very carefully in order for it not to break, and it should be followed up by a very hydrating hair moisturizer that doesn't contain mineral oil, paraffin, petrolatum, or protein.
Protein doesn't always say protein, so I've included this list of ingredients that are actually a form of protein, so double-check your moisturizers to make sure they do NOT have protein in them and check your conditioner to make sure they DO have protein in them.
Cocodimonium hydroxypropyl hydrolyzed casein
Cocodimonium hydroxypropyl hydrolyzed collagen
Cocodimonium hydroxypropyl hydrolyzed keratin
Cocodimonium hydroxypropyl hydrolyzed rice protein
Cocodimonium hydroxypropyl hydrolyzed silk
Cocodimonium hydroxypropyl hydrolyzed soy protein
Cocodimonium hydroxypropyl hydrolyzed wheat protein
Cocodimonium hydroxypropyl silk amino acids
Cocoyl hydrolyzed collagen
Cocoyl hydrolyzed keratin
Hydrolyzed keratin
Hydrolyzed oat flour
Hydrolyzed silk
Hydrolyzed silk protein
Hydrolyzed soy protein
Hydrolyzed wheat protein
Keratin
Potassium cocoyl hydrolyzed collagen
TEA-cocoyl hydrolyzed collagen
TEA-cocoyl hydrolyzed soy protein