\The use of hand-free sanitizers has steadily increased over the past decade. Their use began in hospitals, doctors' offices, clinics and medical facilities. Then we began to see dispensers at building entrances, by elevators and in many public areas. Due to the recent COVID pandemic, the use of hand-free sanitizers has grown exponentially. Dispensers are being placed at the entrance of most stores and in multiple locations in each store. Hand sanitizers are no longer only sold in pharmacies, but can be found everywhere, including hardware stores. Instead of the usual 12- to 16-ounce containers, a gallon of sanitizing hand sanitizer can be purchased at a time.
In the United States, hand sanitizers are also known as "consumer sanitizer wipes" and are regulated by the Food and Drug Administration (FDA). They are considered over-the-counter (OTC) drugs and are part of the Consumer Antiseptic Wipe Product Monograph. This monograph has not yet been finalized, but tentative final monographs have been published in the Federal Register in 2016, 2017, and 20191,2,3. The latest tentative final monograph does not classify any active substance as Class I (safe and effective). However, it classifies three actives as Class III (safety and efficacy requires additional data). These activities are
Alcohol (denaturing) at 60-90%.
Isopropyl alcohol at 70-91.3%.
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The monograph requires marketers of such products to test the safety and efficacy of the product. Efficacy should be tested in vitro and in vivo. In vitro testing entails a series of antimicrobial tests using certain bacterial strains to determine the antimicrobial activity of the antimicrobial active substance. Three tests are recommended in the monograph, namely the minimum inhibitory concentration (MIC), the minimum bactericidal concentration (MBC), and the time-kill test for certain strains of bacteria. For in vivo trials, the monograph provides for two clinical studies at two independent centers, each enrolling at least 100 people, to assess efficacy. Efficacy is typically assessed using the log reduction in bacteria following product application compared to placebo.
As a result of the recent COVID pandemic, the FDA issued interim guidance for the manufacture of alcohol-based hand sanitizers.4 The guidance allows FDA-registered manufacturers to produce alcohol-based hand sanitizers based on the following formulations.
Alcohol (formulated as 80% v/v denatured ethanol) in aqueous solution or isopropyl alcohol (formulated as 75% v/v) in aqueous solution
Glycerol 1.45% v/v
Hydrogen peroxide (0.125% v/v)
Sterile distilled water or boiled cold water
The stipulation is that no other additives, including fragrances, should be added to this formulation. The formulation should not be thickened, but should be in solution form only. The formulation should also not be used as a foam or aerosol.
Formulating hand sanitizer free
Now for the interesting stuff about formulating hand sanitizer-free products. The primary method of dispensing hand-free sanitizer in most facilities is a motion-sensitive foam dispenser. These dispensers usually contain an alcohol solution that foams up when dispensed. The formula contains 70% alcohol for sanitizing and PEG-12 polydimethylsiloxane as the foaming agent. It also contains glycerin (a well-known moisturizer), tocopheryl acetate and several esters to replenish skin lipids, as well as a mild fragrance to mask the alcohol odor.
The second most popular form of hand-free lotion on the market is the gel. Most gels are formulated with an alcohol content between 60-80%. Many gels are thickened with carbomer or acrylate variants (e.g. acrylate/C10-30 alkyl acrylate cross-linked polymers). Due to the high alcohol content in these formulations, it is generally not recommended to neutralize carbomer with sodium hydroxide. Typically, it is recommended to neutralize acrylate polymers with organic amines. The formulator used triethanolamine, triamine and aminomethyl propanol. Using acrylates to make gels offers good cost advantages and helps form crystal clear gels. Because acrylates cannot handle the residual salts in their hands, the product usually breaks up during the wipe-off process. Due to the recent attacks on acrylates by various organizations and their potential labeling as microplastics, many formulators have turned to cellulose as a rheology modifier. Cellulose is of natural origin and can also thicken alcohol-based formulations. The most commonly used thickening agent is hydroxypropyl cellulose, followed by hydroxyethyl cellulose. Cellulose will produce a clear gel and give the formulation a slippery feel. The cellulose gel does not need to be neutralized and will not break when rubbed on the hands. Cellulose will produce a clear gel and give the formulation a slippery feel.
Alcohol-free hand sanitizers typically capture a small segment of the market by targeting some customers who do not like to use alcohol. These products are based on benzalkonium chloride and come in a variety of forms, such as lotions, gel creams and gels. Being alcohol-free, these products can be considered halal if they meet the remaining criteria required for certification.
A myriad of ingredients can often be added to hand-free liquid gels. Glycerin is very popular because it helps moisturize the skin and changes the feel and application of the gel. Aloe vera is another ingredient commonly added to formulations because of its well-known healing and soothing properties. Several alcohol-soluble esters are also used. esters of alpha-hydroxy acids are popular because of their high polarity and ease of incorporation into such formulations. Such esters are lauryl lactate, myristyl lactate and C12-15 alkyl lactate. Other alcohol compatible esters with high polarity include diisopropyl adipate and isodecyl neopentanoate.
An important key ingredient present in most gels is fragrance. Choosing a fragrance for a hand-free gel is not simple. It is important to ensure that the fragrance remains stable at such high alcohol concentrations during the accelerated stability period (typically 3 months at 45°C). In addition, since many professionals use the product more than 10 times a day, the fragrance must mask the alcohol odor without being overpowering.
When checking the stability of such formulations, it should not be forgotten to store them in explosion-proof ovens. These formulations are very flammable and can cause a fire if stored in a regular laboratory oven. The compatibility of these formulations with the final packaging should also be tested, as high concentrations of alcohol can distort many types of plastics.
I hope this quick review of hand-free liquid formulations has been very helpful to formulators and will put them one step ahead of the curve when formulating such products. It is now up to the individual formulator to be creative and add his/her personal touch to make such formulations unique in this crowded undifferentiated market.
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