A comb is a device made of solid material, generally flat, always toothed, and is used in hair care for straightening and cleaning hair or other fibers.

The etymology of the English word is ancient, going straight back to Proto-Indo-European roots meaning "tooth", "toothed", "to bite", and found in ancient Greek and Sanskrit.

Combs are among the older tools known to mankind, having been found in very refined forms already in settlements dating back to 5000 years ago in Persia — possibly at the height of the first major Indo-European migrations.

The term is applied in English also to

• the fleshy crest atop the head of many species of birds (hens et al.)
• the ridge or reinforcement in the same position on steel helmets
• a periodic, sharp spike or dip pattern in a signal
• the thick, semi-flexible water-filtering structures used in filter-feeding by baleen whales, which are if anything closer to what one would call "brushes".

Alternative uses of combs include:

• Keeping long hair in place.
• Decorating the hair.
• Keeping a kippa in place.
• Separating cotton fibers from seeds and other debris. The cotton gin, a mechanized version of the comb, is one of the machines that ushered the Industrial revolution.
• Making music, by dramatically increasing the high-frequency harmonic content of the hum produced by the human voice box, and modulating the resulting spread sound spectrum by changing the resonanting frequency of the oral cavity. This is accomplished by stringing a plant's leaf or a piece of paper in one side of the comb and humming with cropped lips on the opposite side. This was the inspiration for the kazoo.

Combs are also a favorite spot for police investigators to collect hair and dandruff samples that can be used in ascertaining dead or living people's identities, as well as their state of health, toxicological profiles, and so forth.

Sharing combs is a common source of parasitic infections, as one user can leave a comb with plenty of eggs or even live parasites, facilitating the transmission of lice, fleas, crabs, mites, fungi, and other undesirables. While these parasitic infestations are usually only mildly uncomfortable, they can also act as a conduit for more serious illnesses, such as the Black Plague, that killed one third of all Europeans in the 14th century. In contrast, specialized combs such as "flea combs" or "nit combs" can be used to remove macroscopic parasites.

Wooden combs are largely made of boxwood, cherry wood, or other pine wood. Good quality wooden combs are usually handmade and polished.

A 2001 book on haircare, Curly Girl (authors: Lorraine Massey, Deborah Chiel; ISBN 0761123008), advocated the use of wide-toothed wooden combs in place of hairbrushes and fine-toothed plastic combs. The authors note that wooden combs are anti-static and have no sharp seams, and therefore are unlikely to snap or tangle hair.

A hairbrush, which is larger than a comb, is also commonly used for shaping, styling and cleaning the hair.

There are no known strictly religious meanings for the use of combs, although these tools are mentioned in various religious scriptures.

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