acetic acid
Meaning of acetic acid: Concentration decides everything: the same molecule flavors food, whitens abnormal tissue during an examination, and burns skin as an industrial liquid.
Definition of acetic acid
Acetic acid is a simple two carbon organic acid, best known as the compound that makes vinegar sour and sharp smelling. Vinegar is a dilute water solution of it. The pure liquid, called glacial acetic acid, is corrosive and is one of the basic feedstocks of the chemical industry, while weak solutions have several ordinary uses in medicine.
Does concentration change what it does?
| Form | What it is | Where it appears |
|---|---|---|
| Vinegar | A dilute water solution | Food, preserving, household cleaning |
| Clinical solutions | Weak solutions prepared for one purpose | Ear drops, examination of the cervix, some wound irrigations |
| Glacial acetic acid | The pure, undiluted liquid | Chemical manufacturing and laboratory work |
Nothing about the molecule changes between those rows. What changes is how many of them are present, and that alone separates a salad dressing from a substance that burns skin and damages the eyes on contact. The same compound is also a normal product of human metabolism and of the bacteria living in the gut, circulating harmlessly as acetate.
How is it used in medicine?
Dilute drops acidify the ear canal, which discourages the bacteria and fungi that thrive in the damp, mildly alkaline conditions of an infected canal. A weak solution is painted onto the cervix during colposcopy and during simple visual screening in settings without laboratory support, where abnormal areas turn white and can then be sampled. The same technique is applied to the vulva, anus and penis when looking for changes linked to human papillomavirus. Industrially the acid is a starting point for other medicines, for plastics such as cellulose acetate, and for countless everyday products.
Why does abnormal tissue turn white?
Acetic acid draws water out of cells and reversibly clumps the proteins inside them, particularly those packed into the nucleus. Cells that are dividing rapidly carry larger, more crowded nuclei, so more protein precipitates in them and the tissue reflects light instead of showing the pink of the blood vessels underneath. The effect fades within minutes. It is a signpost rather than a diagnosis: healing tissue, ordinary immature cells and simple inflammation whiten too, so anything that turns white is examined rather than assumed to be abnormal.
Also known as
Used in a sentence
A dilute acetic acid solution was applied during the examination to help identify abnormal tissue.
Good to know
Dilute acetic acid solutions used clinically are far weaker than the concentrated industrial chemical, a distinction that matters because concentration determines whether the substance is mild or corrosive.
Word origin
Where “acetic acid” comes from
From Latin acetum, meaning vinegar.