Protein or the physical region of the protein that participates in chemical catalysis. In solution proteins also undergo variation in structure through thermal vibration and the collision with other molecules. Proteins can be informally divided into three main classes, which correlate with typical tertiary structures: globular proteins, fibrous proteins, and membrane proteins. Almost all globular proteins are soluble and many are enzymes. Fibrous proteins are often structural, such as collagen, the major component of connective tissue, or keratin, the protein component of hair and nails. Membrane proteins often serve as receptors or provide channels for polar or charged molecules to pass
Hair removal been used in attempts to eradicate lice or to minimize body odor due to accumulation of odor-causing micro-organisms in hair. Some people with trichiasis find it medically necessary to remove ingrown eyelashes. Shaving against the grain can often cause ingrown hairs. Many forms of cancer require chemotherapy, which often causes severe and irregular hair loss. For this reason, it is common for cancer patients to shave their heads even before starting chemotherapy. In extreme situations people may need to remove all body hair to prevent or combat infestation by lice, fleas and other parasites. Such a practice was used, for