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.
Trace Minerals International established reference ranges for nails in the 1980s.
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.
Biological materials are widely used as a bioindicator for environmental Pollution with heavy metals. Among These are hair and nails, which are also recommended by the World Health Organization (WHO) for worldwide environmetal Monitoring. Heavy metals Cd, Cu, Pb and Zn were determined in fingernails and scalp hair from different sexes and ages of school children, adults and workers from polluted and unpolluted Areas of Aswan, Egypt. The results reveal that people living in polluted Areas show higher concentration of metals in nails and hair. The study proves that nails and hair can be used successfully as biological indicators for the assessment of heavy metal Pollution.
The above excerpt is from the research paper by Rashed MN and Hossam F: HEAVY METALS IN FINGERNAILS AND SCALP HAIR OF CHILDREN, ADULTS AND WORKERS FROM ENVIRONMENTALLY EXPOSED AREAS AT ASWAN, EGYPT