A hair iron or hair tong is a tool used to change the structure of the hair with the help of heat. There are two general kinds. Straightening irons, used to straighten the hair, and curling irons, used to make the hair curly. Straightening irons may also be called flat irons, but not to be confused with clothes flat irons. Context usually can separate the two.

Hair straighteners: The first hair straightener was invented by Madame C. J. Walker using chemicals of scalp preparation and lotions to straighten the hair. Unfortunately, using this invention soon led to damaged, scorched hair from all the chemicals that were added, but as technology improved, so did the hair straighteners. Years later, M. Marcel Grateau invented heated metal hair care implements such as hot metal combs. Using the metal hair care, the straightener slid easier through the hair, causing less damage and dryness as previously used techniques. After this invention, ceramic and electrical straighteners were introduced, allowing adjustment of heat settings and straightener size. Another method of hair straightening is Japanese Hair Straightening, which acts as a sort of "anti-perm" and is available at most salons. A new trend is the use of tourmaline being crushed into irons and other hair appliances since they generate many negative ions which have positive effects on hair. Most high end salon or professional brands use tourmaline and/or ceramic hair irons.

Less expensive brands may use aluminum plates, however aluminum is not as good for the hair, and is less effective. Higher quality irons use ceramic plates and even higher quality hair straighteners use ceramic tourmaline plates.

A number of products may be used to stop the hair from drying when it is straightened. Straightening may cause split ends and thinning of the hair.

Hair straighteners must never be used on wet hair unless they are specified as wet to dry straighteners. Even then the hair cannot be soaking wet.

As well, there are several different types of hair straighteners, such as ionic, ceramic, and glass.

Hair