Etidronic acid

Etidronic acid (INN) or etidronate disodium (trade name Didronel®) is a bisphosphonate used to strengthen bone, treat osteoporosis, and treat Paget's disease of bone.

Chelating Agent and Anti-oxidant
Etidronic acid is a chelating agent and may be added to bind or, to some extent, counter the effects of substances, such as arsenic, iron, or other metal ions (that can occur in the presence of some soaps), which may be discharged as a component of grey wastewater and could conceivably contaminate groundwater supplies. Etidronic acid also acts to retard rancidification and oxidation of fatty acids. While etidronic acid has not been limited from inclusion in cosmetics and does have legitimate uses, it is recommended that, as with most cosmetic products (particularly soaps), the product should be thoroughly rinsed from the skin after use.

Etidronic acid is listed as an ingredient of several cosmetic formulations. Several examples of Etidronic acid's presence in soap products are: Propolis soap, Dove body wash, Axe body wash, Lever 2000 body wash, Yardley of London, Johnson and Johnson's Lavender, Chamomile Creamy Baby Soap bar and Tesco Pure Soap bar.

Etidronic acid is also included among swimming pool chemicals. It is used as a stain inhibitor to prevent metal ions coming out of solution and staining the sides of swimming pools.