Occasionally borrowing a friend’s stick or roll-on product might seem like a harmless convenience in a rush. However, the intimate nature of these personal hygiene products, which are applied directly to the skin’s surface, means that using someone else’s can carry several unintended biological and chemical consequences. The potential issues range from the transfer of microorganisms to unexpected skin reactions and, ultimately, a failure of the product to work effectively for you.
Transferring Bacteria and Fungi
The armpit harbors a microbial community that is slightly different for every person. When a solid stick or roll-on applicator is swiped across the skin, it picks up bacteria, fungi, and dead skin cells from the user’s underarm. Applying a borrowed deodorant can directly transfer a portion of the original owner’s skin flora to your own.
The transferred microorganisms may include strains of odor-causing bacteria or fungi that are foreign to your body. Sharing a product can potentially transmit common skin irritants like certain Staphylococcus species, which can cause folliculitis, or fungal spores that may lead to minor infections such as ringworm. This risk is elevated if the product is applied immediately after shaving, as microscopic cuts in the skin can provide an entry point for these transferred microbes. Antiperspirants can sometimes harbor more germs than deodorants, which often contain antimicrobial ingredients.
Skin Sensitivity and Ingredient Reactions
You may still react negatively to a borrowed product’s chemical formulation. The armpit skin is thin and sensitive, making it vulnerable to irritation from common deodorant and antiperspirant ingredients. This unexpected reaction is a form of contact dermatitis, which can manifest in two distinct ways.
Irritant contact dermatitis is the more common reaction, often causing immediate stinging, redness, or burning upon application. This reaction is frequently triggered by ingredients like high concentrations of alcohol or the acidic nature of aluminum compounds found in many antiperspirants. Natural deodorants are not immune, as the alkaline nature of baking soda or certain essential oils can also disrupt the skin’s natural pH balance and cause irritation.
The second type, allergic contact dermatitis, is an immune-system response that is usually delayed, appearing as an itchy, scaly rash a day or two after exposure. The most prevalent allergen in these products is fragrance. Other common allergens include preservatives like parabens and propylene glycol, all of which can cause an inflammatory response in a sensitive individual.
How Effectiveness is Compromised
A borrowed product might simply fail to perform the function you need it to. Deodorants and antiperspirants work through different mechanisms, and their efficacy is closely tied to an individual’s unique body chemistry and sweat rate. Antiperspirants use aluminum salts to form a temporary plug in the sweat ducts to reduce wetness, while deodorants primarily use antimicrobial agents to neutralize the bacteria that feed on sweat and produce odor.
If you are a heavy sweater accustomed to an antiperspirant, borrowing a pure deodorant will likely result in inadequate wetness protection. Furthermore, the specific bacteria strains in your armpit have adapted to your usual product, which has shaped your personal armpit microbiome. Introducing a new formulation, with different active ingredients, may not be effective against your particular odor-causing microbes, meaning the borrowed product might not control odor or wetness as expected.