The purpose of a conditioner is to make hair easy to comb, easy to style and give hair an attractive gloss after shampooing. Some shampoos have an added conditioner, or a conditioner may be applied separately following the shampoo. Conditioners can be categorized in several ways:

• Cationic detergents-most commonly quaternary ammonium compounds, they are ingredients in both shampoos and hair conditioners. They effectively restore roughened cuticle and decrease static electricity in newly shampooed hair. Cationic detergents are a good choice in shampoo and conditioner for persons with dyed or permanent-waved hair.
• Film forming conditioning agents-also called "hair thickeners"; they are polymer agents such as polyvinylpyrrolidone (PUP). The polymer fills defects in the hair shaft, enhances hair gloss and reduces static electricity. The polymer coating thickens the hair shaft; for this reason, film-forming conditioners are not appropriate for fine hair because the added thickness and weight makes the hair difficult to style.
• Protein conditioning agents-contain animal protein that is able to enter the hair shaft. This provides a temporary strengthening of hair shafts that have been damaged or "weathered".

Conditioners are further identified in the following categories:

• Instant - applied immediately after shampooing and then rinsed out
• Deep Conditioning - left in the hair for up to 30 minutes after shampooing to enhance hair-shaft repair-protein conditioning agents are often ingredients in "deep" conditioners
• Leave-in - by definition are to be left in the hair until the next shampoo. Leave-in conditioners may be especially useful for kinky hair to aid in hair styling.