It is the second most abundant trace metal in humans after iron and it is the only metal which appears in all enzyme classes.In proteins, zinc ions are often coordinated to the amino acid side chains of aspartic acid, glutamic acid, cysteine and histidine. The theoretical and computational description of this zinc binding in proteins (as well as that of other transition metals) is difficult.Roughly 2–4 grams of zinc are distributed throughout the human body. Most zinc is in the brain, muscle, bones, kidney, and liver, with the highest concentrations in the prostate and parts of the eye. Semen is particularly rich in zinc, a key factor in prostate gland function and reproductive organ growth.Zinc homeostasis of the body is mainly controlled by the intestine. Here, ZIP4 and especially TRPM7 were linked to intestinal zinc uptake essential for postnatal survival.In humans, the biological roles of zinc are ubiquitous. It interacts with "a wide range of organic ligands", and has roles in the metabolism of RNA and DNA, signal transduction, and gene expression. It also regulates apoptosis. A review from 2015 indicated that about 10% of human proteins (~3000) bind zinc, in addition to hundreds more that transport and traffic zinc; a similar in silico study in the plant Arabidopsis thaliana found 2367 zinc-related proteins.In the brain, zinc is stored in specific synaptic vesicles by glutamatergic neurons and can modulate neuronal excitability. It plays a key role in synaptic plasticity and so in learning.
For men who are required to, or simply prefer to shave, studies show the optimal length to be about 0.5 mm to 1 mm to prevent the hair growing back into the skin. Using a beard trimmer at the lowest setting (0.5mm or 1mm) instead of shaving is an efficient alternative. The resulting faint stubble can be shaped using a standard electric razor on non-problematic areas (cheeks, lower neck).For most cases, completely avoiding shaving for three to four weeks allows all lesions to subside, and most extrafollicular hairs will resolve themselves within at least ten days. Permanent removal of the hair follicle is the only definitive treatment for PFB. Electrolysis is effective but limited by its slow pace, pain and expense. Laser-assisted hair removal is effective. There is a risk of skin discoloration and a very small risk of scarring.Some men use electric razors to control PFB. Those who use a razor should use a single blade or special wire-wrapped blade to avoid shaving too closely, with a new blade each shave. Shaving in the direction of hair growth every other day, rather than daily, may improve pseudofolliculitis barbae. If one must use a blade, softening the beard first with a hot, wet washcloth for five minutes or shave while showering in hot water can be helpful. Some use shaving powders (a kind of chemical depilatory) to avoid the irritation of using a blade. Barium sulfide-based depilatories are most efficient, but produce an unpleasant smell. Treatment
The simplest treatment for PFB is to let the beard grow.