Alizarin is an anthraquinone is an organic compound that has been used as a red dye, principally for dyeing textile fabrics since ancient times. Historically it was derived from the roots of the madder plant Rubia tinctorum, in which it occurs combined with the sugars xylose and glucose. Laboratory methods of preparing alizarin from anthraquinone were discovered in 1868, and, upon commercial introduction of the synthetic dye in 1871, the natural product disappeared from the market for textile dyes. At present alizarin is commonly used in biomedical studies involving bone growth, osteoporosis, bone marrow, calcium deposits in the vascular system, cellular signaling, gene expression, tissue engineering, and mesenchymal stem cells. Alizarin precipitates free calcium, and tissue block containing calcium stain red immediately when immersed in alizarin. It is approved by FDA as a Calcium test system for clinical chemistry. Alizarin red, has been used for a quantitative sweat measure to characterize the sweat distribution in patients with syncope, anxiety, and POTS.