The dosage of 1–10 mg/L is preferred as scale inhibitor, 10–50 mg/L as corrosion inhibitor, and 1000–2000 mg/L as detergent. Usually, HEDP is also used together with polycarboxylic acid (superplasticizer), in which it acts as reducing agent. Chelating agent and antioxidant
Etidronic acid is a chelating agent and may be added to bind or, to some extent, counter the effects of substances, such as calcium, iron or other metal ions, which may be discharged as a component of grey wastewater and could conceivably contaminate groundwater supplies. As a phosphonate it has corrosion inhibiting properties on unalloyed steel. Etidronic acid also acts to retard rancidification and oxidation of fatty acids. HEDP and its salts are added to detergents and other cleaning agents to prevent the effects of hard water. It is also used in peroxide bleaching to prevent degradation of peroxides by transition metals. Etidronic acid is listed as an ingredient of several cosmetic formulations where it is used for suppressing radical formation, emulsion stabiliser and viscosity control. 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 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. Etidronic acid is used in bars of soap.
A sequela (UK: , US: ; usually used in the plural, sequelae ) is a pathological condition resulting from a disease, injury, therapy, or other trauma. Derived from the Latin word, meaning “sequel”, it is used in the medical field to mean a complication or condition following a prior illness or disease.A typical sequela is a chronic complication of an acute condition—in other words, a long-term effect of a temporary disease or injury—which follows immediately from the condition. Sequelae differ from late effects, which can appear long after—even several decades  after—the original condition has resolved. In general, non-medical usage, the terms sequela and sequelae mean consequence and consequences. Examples and uses
Chronic kidney disease, for example, is sometimes a sequela of diabetes; "chronic constipation" or more accurately "obstipation"  (that is, inability to pass stool or gas) is a sequela to an intestinal obstruction; and neck pain is a common sequela of whiplash or other trauma to the cervical vertebrae. Post-traumatic stress disorder may be a psychological sequela of rape. Sequelae of traumatic brain injury include headache, dizziness, anxiety, apathy, depression, aggression, cognitive impairments, personality changes, mania, and psychosis. COVID-19 is also known to cause post-acute sequelae, known as long COVID, post-COVID syndrome, or post-acute sequelae of COVID-19 (PASC). This refers to the continuation of COVID-19 symptoms or the development of new ones, four or more weeks after the initial infection; these symptoms may persist for weeks and months.