Isopropyl Alcohol

Overview

Isopropyl alcohol (IPA) is a small-molecule alcohol widely used as a solvent and disinfectant. It is closely related to ethanol but has slightly different solvent properties and a more pronounced “rubbing alcohol” odour.

In DIY cosmetic formulation, IPA is almost never an in-formula ingredient. It is harsh on skin compared to ethanol, has a stronger odour, and has no functional advantage over ethanol in leave-on cosmetics. The reason it appears in cosmetic supplier catalogues is for its essential role in workspace and equipment sanitation — disinfecting beakers, mixing vessels, lab equipment, and work surfaces between formulation batches.

The two common cosmetic-supplier grades:

• 70% IPA (with 30% water) — the disinfection sweet spot. The water content slows evaporation enough that the alcohol contacts microbes long enough to kill them. The standard for surface sanitation.
• 99.8% IPA (anhydrous) — pure solvent grade. Evaporates very fast (less effective for surface disinfection) but excellent for dissolving residues, cleaning electronic equipment, and use as a solvent in alcohol-based products. Often what is sold as “Isopropyl Alcohol (99.8%)” in cosmetic supplier catalogues.

Shelf life is essentially indefinite stored sealed and cool.

What it does in a formula

Real uses in cosmetic formulation:

• Equipment sanitation (70% IPA) — wipe down beakers, scales, mixing vessels, work surfaces between batches. Essential for hygiene; some preservative-related batch failures trace back to poor equipment sanitation.
• Workspace sanitation — same role, larger scale.
• Dissolving and cleaning (99.8% IPA) — removes oily residues from glass and metal equipment; cleans precision parts of homogenisers and emulsifiers.
• Wax and balm prototyping — dissolves wax residue from equipment after working with heavy balms.
• Mould preparation in soap-making — light IPA spray on silicone moulds before pour helps with release in some recipes.

What it is NOT used for in DIY cosmetics:

• Leave-on cosmetic skin ingredient — too harsh, too smelly. Ethanol (denatured cosmetic alcohol) is the standard.
• Preservative — neither 70% nor 99.8% IPA is a leave-on cosmetic preservative.
• Hand sanitiser at home production — possible, but requires careful WHO-compliant formulation. Most home formulators use ethanol-based formulas.

How to use

For equipment sanitation: spray 70% IPA on the surface or equipment, let dwell 30 seconds minimum, wipe with clean lint-free cloth.

For deep cleaning: 99.8% IPA on a lint-free cloth to dissolve stubborn residues.

Always store away from open flame (IPA is flammable), in clearly labelled bottles, and out of reach of children.

Best for / Worst for

Best for: equipment sanitation between formulation batches, workspace cleaning, residue removal from glass and metal, lab-style cosmetic formulation hygiene.

Worst for: in-formula use in leave-on cosmetics, hand sanitisers (use ethanol-based instead), formulations marketed as “alcohol-free” (any alcohol content would void the claim), skin application without dilution.

Common pitfalls

Confusing 70% and 99.8% grades for surface disinfection. Counter-intuitively, 70% IPA is a better surface disinfectant than 99.8% because the water content slows evaporation, giving more contact time with microbes. Use 70% for surfaces, 99.8% for solvent applications.

Using IPA in skincare formulas. This is a recipe-source confusion that comes up periodically. If a recipe calls for “alcohol,” it almost certainly means cosmetic-grade ethanol (denatured ethanol), not isopropyl alcohol. They are not interchangeable.

Flammability. Both 70% and 99.8% IPA are flammable. Keep away from open flame, hot plates, and any source of ignition during use.

Workspace odour. IPA evaporation produces a strong solvent smell that lingers in poorly ventilated spaces. Ventilate properly when using large quantities.

Hand sanitiser shortcut. During the 2020 pandemic many home formulators tried to make hand sanitiser from IPA. The result is often harsh, smelly, and not as effective as a properly formulated WHO-style ethanol-based product. Stick to ethanol-based formulas for hand sanitiser.

Substitutes

For equipment sanitation:

• Cosmetic-grade ethanol (96%) — equally effective surface disinfection, less harsh smell, more expensive.
• Hydrogen peroxide (3%) — alternative surface sanitiser, useful for some materials, slower-acting.
• Sodium hypochlorite (dilute bleach) — for floors and heavy-soil surfaces, not safe for equipment.

For in-formula alcohol use (which IPA is NOT for):

• Denatured cosmetic alcohol — the standard for leave-on cosmetic alcohol content.
• Cosmetic-grade ethanol (96%) — when undenatured is required.
• Witch hazel hydrosol (witch-hazel-hydrosol) — for natural toners with a mild alcohol content.