Your hair is mostly made of water. To be shiny and supple, your hair needs to be adequately hydrated. You lose water from the sun, too much processing, and blow- drying. Oil from your scalp coats each shaft and acts as a barrier against evaporation. Your hair also needs proper blood circulation to remain strong, which can be increased with ordinary and hold hair conditioner. Hair consists of roughly 97% of a protein called keratin. Keratin is on its surface rich in negatively-charged amino acids. Hair conditioners therefore often contain cationic surfactants, which don't wash out completely, because their hydrophilic ends strongly bind to keratin. The hydrophobic ends of the surfactant molecules then act as the new hair surface. Hair conditioners agents are also called moisturizers in some cases and usually are composed of various oils and lubricants (e.g., some fatty alcohols, panthenol, dimethicone, etc.). They also contain antistatic agents, and sequestrants for better function in hard water and used in pack and leave-in hair conditioner. Other additional chemicals are preservatives (usually parabens). Hair conditioners are frequently acidic, as low pH protonates the amino acids, providing the hair with positive charge. This allows better forming of hydrogen bonds between the keratin scales, giving the hair more compact structure. Citric acid, or other organic acids, is the usual component maintaining acidity. There are several groups of hair conditioners, differing with composition and main functionality aspects: Moisturizers, whose role is to hold moisture in the hair. Usually contain higher proportion of humectants. Reconstructors, usually containing hydrolyzed protein. Ordinary and hold hair conditioner's role is to penetrate the hair and strengthen its structure. Acidifiers, acidity regulators which maintain the conditioner's pH at about.5-3.5. In contact with acidic environment, the hair's somewhat scaly surface tightens up, as the hydrogen bonds between the keratin molecules get strengthened. Detanglers, modifying the hair surface by pH as acidifiers, and/or by coating it with polymers, as glossers Pack and leave-in hair conditioner, thermal protectors, usually heat-absorbing polymers, shielding the hair against excessive heat, caused by, e.g., blow-drying or curling irons or hot rollers. Glossers, light-reflecting chemicals binding to the hair surface. Pack and leave-in hair conditioner, heavy and thick, with high content of surfactants able to bind to the hair structure and "glue" the hair surface scales together. These are usually applied to the hair for longer time. The surfactants are based on long straight aliphatic chains similar to saturated fatty acids. Their molecules have tendency to crystallize easily, giving the conditioner higher viscosity, and they tend to form thicker layers on the hair surface. Pack and leave-in conditioner, thinner, containing different surfactants, adding only a little material to the hair. Hair conditioners are based on unsaturated chains, which are bent rather than straight. This shape makes them less prone to crystallizing, making a lighter, less viscous mixture and providing significantly thinner layer on the hair. The difference between leave-in and pack conditioners is similar to the difference between fats and oils. Ordinary and hold hair conditioner, combining some aspects of both pack and leave-in ones.