Basic Cosmetic Formulations - Deodorant Sticks
Article submitted by Gary Neudahl
In a previous post, the composition of an antiperspirant deodorant (APDO) stick was presented. In this post we’ll look at the typical composition of a deodorant stick, which is very different from that of an APDO stick.
Here’s the typical composition of a deodorant stick, presented from highest to lowest average concentration:
- Hydrophilic Carriers: 50—80%
- Water: 15—20%
- Gelling Agents (Gellants): 5 — 8%
- Clarifying Agents/Solubilizers: 0 — 6%
- Antimicrobial Agents: 0 — 2%
- Fragrance (Parfum): 0 — 2%
- Chelating Agents (Chelants): 0 — 0.1%
- Neutralizing Agent 0 — 0.01%
- Anti-oxidants 0 — 0.01%
- Colorants 0 — 0.001%
The primary carrier system for deodorant sticks today usually consists of one or more glycols, such as Propylene Glycol and/or Dipropylene Glycol, with a judiciously selected amount of water (aqua). Before the regulation of volatile organic compounds (VOCs), specially denatured alcohol (SD Alcohol; alcohol denat.) was typically used instead of glycols. This allowed an immediate antimicrobial action, and immediate cooling sensation, which was great for the guys, but it also presented the potential for irritation, especially if the underarms were recently shaved, which was not so wonderful for the gals! Some deodorant sticks with Alcohol denat. and Propylene Glycol remain available and are, not surprisingly, marketed to men.
This primary carrier system is gelled using Sodium Stearate. That’s what the INCI name is, but it’s not your usual analytical grade material! The alcohol-containing sticks commonly utilize what is essentially the sodium salt of triple-pressed grade stearic acid. That is, this “Sodium Stearate” is actually primarily Sodium Palmitate with a somewhat lesser amount of Sodium Stearate. It is ideal for optimizing the clarity of the sticks. The composition of the Sodium Stearate that is used for glycol-based sticks is even more complex. Because the gelling properties of the Sodium Stearate used for the alcohol-based sticks proved suboptimal for glycol-based sticks, its composition was further adapted to achieve the desired esthetics and gelling properties. The result is a “Sodium Stearate” that contains appreciable amounts of Sodium Palmitate, Sodium Stearate, Sodium Arachidate and Sodium Behenate. The sticks that result usually aren’t as clear, but they provide superior set point and payoff (or do you say payout?) characteristics.
Clarifiers and/or solubilizers may be used to promote stick clarity and reduce the potential for syneresis, particularly when high levels of fragrance are utilized. Nonionic surfactants of moderate to high hydrophilic-lipophilic balance (HLB), such as PPG-3 Myristyl Ether or Isosteareth-20, may be utilized.
Antimicrobials are sometimes added to inhibit the growth of microorganisms in the armpits. This can help with the reduction of axillary malodor since certain bacteria metabolize sweat and sebum into volatile, malodorous substances. Triclosan remains the most commonly used antimicrobial, although continuing bad press has resulted in its removal from some products and the adoption of alternatives including specially selected botanical extracts and silver chloride.
Fragrance (parfum) is frequently used in deodorants and, in the absence of antimicrobials or fragrant and/or antimicrobial essential oils, it is solely responsible for the “deodorizing” effect of the product. The base used by the perfume house for a deodorant stick fragrance oil is likely to differ appreciably from that used for emulsion-based products since there is no oil phase in which to dissolve the fragrance oil. Hence, it is likely to be more polar.
Chelating Agents, such as Disodium EDTA or Tetrasodium EDTA, may be used to tie up multivalent ions that become part of the composition, particularly through the water supply, but also through aqueous or glycolic extracts. Many of these ions can promote the oxidation of unsaturated ingredients (substances with carbon-carbon double bonds). By making the metal ions inactive, the chelants enhance fragrance stability and so extend product shelf life.
Neutralizing Agents are occasionally added to improve stick clarity and/or ensure that the desired pH for the deodorant stick (typically about 9) is met. The Sodium Stearate sold as gellants for deodorant sticks typically has a small amount of free fatty acid present. This limits the alkalinity of the deodorant stick, but it can also result in a haze from the free acid. Alkalis that may be used to neutralize the free fatty acid include Aminomethyl Propanol, Poloxamine 1307, Sodium Hydroxide and even Tetrasodium EDTA (yes, it can be bifunctional!).
An anti-oxidant, most commonly BHT, may be added as an alternative or as a supplement to the stabilizing effects of chelants. Again, then intent is to extend shelf life by reducing oxidative processes.
Colorants may be added at very low level for their esthetic benefits. The use levels of these water or alcohol soluble dyes are so low that skin and fabric staining are rarely a legitimate concern.
Regulation of deodorants
I’d like to make one other comment, from a regulatory perspective, as it affects the manufacturing processes and marketing claims that are allowed. The intended purposes of deodorants are by definition cosmetic (“intended to be rubbed, poured, sprinkled, or sprayed on, introduced into, or otherwise applied to the human body…for cleansing, beautifying, promoting attractiveness, or altering the appearance” [FD&C Act, sec. 201(i)]). The intended purposes of APDOs are not purely cosmetic, but also drug-like, by definition (“intended to affect the structure or any function of the body of man” [FD&C Act, sec. 201(g)(1)]). So it is significantly easier to bring a deodorant than an antiperspirant deodorant to market.
And that’s it until next time!