Basic Cosmetic Formulating – Antiperspirant

This is a guest post by Gary Neudahl.

In personal care, there are cosmetics and there are toiletries. What’s the difference? In general, a cosmetic is intended to beautify the body; a toiletry is intended to care for the body. Among toiletries, let’s take a look at Antiperspirant Deodorants (APDOs in industry shorthand) sticks.

APDOs are made with an astringent substance (typically an acidic aluminum-based salt) that, when applied to the underarms, reduces perspiration and concurrently inhibits microbial growth for reduced malodor generation. Sticks, gels, soft solids, roll-ons, pads and sprays are typical product forms. They are usually scented for additional malodor protection.

APDO stick formula

Here’s the typical composition of an APDO stick:

Volatile Carriers 15—45%
Co-Gellants 14—18%
Active Ingredients 10—25%
Non-Volatile Carriers 8—20%
Gelling Agents Gellants 4—8%
Clarifying Agents/Solubilizers 0—5%
Feel Modifiers 0—4%
Fragrance (Parfum) 0—0.5%
“Label-Copy” Ingredients 0—0.5%
Antioxidants 0—0.05%

Ingredients

The most commonly used volatile carrier is Cyclopentasiloxane, a cyclic silicone fluid that evaporates about one-sixth as rapidly as water, with virtually no cooling effect due to its low heat of vaporization.

The typical co-gellant is Stearyl Alcohol, with a specific chainlength distribution (mainly C18) that inhibits stick crystallinity.

A commonly employed active ingredient is Aluminum Zirconium Tetrachlorohydrex Gly, which provides good efficacy.

Nonvolatile carriers, which contribute to product skin feel and also reduce or prevent a whitening effect on skin, may include mineral oil, vegetable oils, and/or esters.

The most commonly used gellant is Hydrogenated Castor Oil. It is not fully hydrogenated (to convert unsaturated Ricinoleic Acid moieties to saturated Hydroxystearic Acid moieties), both to control melt point and further inhibit crystallinity. Due to its residual unsaturated content, antioxidants may be added to extend shelf life.

An emulsifier and/or solubilizer may be used to help incorporate the fragrance and to extend shelf life. It also helps with removal of the product from skin during cleansing and from clothing during laundering. PEG-8 Distearate is such an emulsifier that is commonly used in APDO stick formulations.

Feel modifiers include particulates such as corn starches and talc, which are added to improve product aesthetics during and after application.

What about “label copy” ingredients? They are ingredients that are added for marketing- rather than performance- based purposes, to increase the likelihood of consumer trial and satisfaction. They are among the hooks that snare consumer interest, although product performance, and scent, are what determine repurchase intent.

Click here for a complete list of the the Cosmetic Formulating Basics series.

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