potassium hydroxide
Meaning of potassium hydroxide: A strong alkali used to make soap, and in the laboratory to dissolve skin so that fungus can be seen under a microscope.
Definition of potassium hydroxide
Potassium hydroxide is a strong alkali, a white solid that dissolves in water to give a highly corrosive solution. Industry uses it to make soap, in batteries and in cleaning products, and small quantities serve as a food additive. In medicine its main role is in the laboratory, where a drop of the solution clears skin, nail or hair samples so fungal threads become visible.
What does the laboratory test involve?
Scrapings are taken from a scaly patch of skin, a crumbling nail or plucked hairs and placed on a glass slide. A drop of the solution is added and the sample is left for a short time, sometimes with gentle warming. The alkali dissolves the keratin that makes up human skin and nail, but leaves the tougher walls of fungal cells intact. What remains under the microscope is a clear field with any fungal threads and spores standing out. The result is available within minutes, which is why it remains in use despite slower methods that identify the exact species.
Why is an alkali burn different from an acid burn?
| Strong acid | Strong alkali | |
|---|---|---|
| Effect on tissue | Forms a coagulated crust | Dissolves fats and proteins into a soapy liquid |
| Depth of injury | The crust limits penetration | Continues deeper over time |
| Pain at first contact | Immediate and severe | Can be deceptively mild at first |
This difference is why exposure of the eye to an alkali is regarded as the more serious of the two, and why injury from a chemical of this kind can progress after contact has ended.
Where else is it encountered?
Soap making is the classic use, producing the softer soaps that a related sodium compound does not. It appears in drain and oven cleaners, in the electrolyte of alkaline batteries, and in the processing of some foods, where it is used to cure olives, to give pretzels their brown crust, and as a controlled additive under a numbered code. Cocoa processed with alkali uses it or a relative to reduce bitterness. The concentration determines the hazard: dilute preparations in food are harmless, while the concentrated solution damages tissue on contact.
How does it relate to other potassium compounds?
The link is only the shared element. Potassium is essential to nerve and muscle function and is present in every cell, but the hydroxide is a caustic industrial chemical rather than a source of dietary mineral. Medicines whose names end in potassium contain the element paired with a different partner entirely and have nothing in common with it beyond that word.
Also known as
Used in a sentence
A potassium hydroxide preparation of the nail clipping showed branching fungal hyphae.
Good to know
Alkali injuries dissolve tissue and continue to deepen after contact ends, unlike acid burns which form a limiting crust, and the potassium in this compound has no dietary significance.