Zinc has been known as an essential trace element for plants, animals and humas, since 1930. The average adult has between 1.5 and 3 g of zinc. About 60% is placed in muscle, 30% in bones, and about 6% in the skin. The highest concentrations of zinc are found in the prostate gland and sperm of males, as well as in leukocytes and erythrocytes. High concentrations of zinc are also found in the retina of the eye, liver, kidney and hair.