Fingernails and toenails are made of a tough protein called keratin. Along with hair and teeth they are an appendage of the skin. These tissues accumulate
metals that circulate in the blood stream, due to the growth pattern both hair and nail reflect past or chronic exposure.

The average nail growth has been noted by different authors between 2-3mm per months, and is considered about 1/3 the growth rate of hair. A complete nail replacement may take between 3 to 6 months, and toenails require 12 to 18 months. The actual growth rate is dependent upon age, gender, season, exercise level, diet, and hereditary factors. Pregnancy causes a change in nail growth as it does in hair growth.

Physiologically, nail can depict the history of recent imbalances. As the American Academy of Dermatology has stated in its webpage, nail has been used as a diagnostic tool since ancient times. Nutrient deficiencies, drug
reaction or poisoning can be located through nail analysis. Nail mineral analysis reflects toxic exposure as it happened during the period of growth.

Micro Trace Minerals established reference ranges for nails in the 1980s.