Oxalic acid occurs naturally in many plants and is also synthesized by the human body. Consumption of large doses of oxalic acid can cause health problems and, if in its pure form, even death.

View a second image of oxalic acid crystallites.

The reason that oxalic acid can be detrimental is that it binds with important nutrients, primarily calcium, and makes them unusable to the body. However, food containing oxalic acid can safely be consumed in moderation. Some of the most common foods with high levels of oxalic acid are chocolate, cabbage, sweet potatoes, peanuts, spinach, cranberries, strawberries and bell peppers. Intake of such items should be limited if a person is suffering from kidney disease, kidney stones, or rheumatoid arthritis.

Prepared synthetically for the first time in 1776, oxalic acid has been found valuable for many industrial uses. The substance is most often utilized as a wood-bleaching agent, but is also exploited as a rust remover, a grinding agent, a laundry rinse, and a calcium remover in wastewater treatment. Imbibing synthetic oxalic acid is extremely dangerous and can cause oral lesions, tremors, convulsions, shock, vomiting, and the dropping of blood pressure to a fatal level.