The question of what ingredients in underarm products might be harmful often begins with understanding the difference between deodorant and antiperspirant. Deodorants are classified as cosmetics by the Food and Drug Administration (FDA) because their primary function is to mask or neutralize body odor using fragrances and antimicrobial agents. Antiperspirants, however, are regulated as over-the-counter drugs because their active ingredients reduce the flow of sweat to the skin’s surface. This functional distinction determines the presence of the most commonly scrutinized ingredients.
The Primary Concern: Aluminum Compounds
The active components in all antiperspirants are aluminum-based salts, such as aluminum chlorohydrate or aluminum zirconium. These compounds work by dissolving in sweat and forming a temporary physical plug just below the surface of the sweat duct. This blockage reduces the amount of perspiration that reaches the skin, making antiperspirants effective at controlling wetness.
The health controversy surrounding antiperspirants involves a suspected link between aluminum exposure and two conditions: breast cancer and Alzheimer’s disease. Concern about breast cancer arose from the theory that absorbed aluminum could mimic the hormone estrogen and promote the growth of hormone-sensitive breast cancer cells. Other theories suggested that aluminum accumulation could contribute to the neurological changes seen in Alzheimer’s disease.
However, large-scale epidemiological studies and major health organizations, including the National Cancer Institute, state there is no convincing scientific evidence establishing a direct causal link between aluminum-containing antiperspirants and breast cancer or Alzheimer’s disease. Research shows that only a tiny fraction of the aluminum applied to the skin is absorbed. The current consensus is that antiperspirant use does not increase the risk of these conditions for the general population.
Despite the lack of a proven link, some research suggests aluminum may be absorbed more readily through recently shaved or damaged skin. Elevated aluminum content has been found in the brains of persons with Alzheimer’s disease, though it remains unclear if this is a cause or an effect. For individuals with severe kidney disease, doctors recommend limiting aluminum exposure because their bodies struggle to properly excrete the compound.
Preservatives and Additives
Many deodorants and antiperspirants contain additives intended to extend shelf life, control bacteria, or provide scent. These ingredients have drawn scrutiny due to their potential to interfere with the body’s hormonal systems, known as endocrine disruption. Endocrine-disrupting chemicals can mimic, block, or interfere with the body’s natural hormones, even at low levels of exposure.
Parabens, such as methylparaben and propylparaben, are widely used as preservatives to prevent the growth of mold and bacteria. They are considered endocrine disruptors because laboratory studies show they can weakly mimic estrogen activity in the body. Although health agencies have approved parabens in small concentrations, concern stems from the cumulative effect of daily exposure from multiple cosmetic products.
Phthalates are additives often used to make fragrances last longer, and they are frequently hidden under the label “fragrance” or “parfum.” These chemicals have been linked to potential reproductive and developmental issues, particularly during sensitive developmental periods. Phthalates have been associated in some studies with changes in male genital development and reproductive issues in adults.
Triclosan, an antibacterial agent, was historically included in some deodorant formulas to kill odor-causing bacteria. Concerns exist regarding its potential to act as an endocrine disruptor by interfering with thyroid hormone function. Furthermore, the widespread use of triclosan has been cited as a contributing factor to the development of antibiotic-resistant bacteria.
Understanding Common Skin Irritants
For many people, the ingredients that cause the most immediate discomfort lead to localized skin reactions, such as rashes, itching, or stinging. This reaction, often a form of contact dermatitis, is a common reason for individuals to switch products. These irritants do not pose a systemic health risk but can make daily use unpleasant.
Propylene glycol is a petroleum-based solvent and humectant used to create a smooth consistency in stick deodorants. While recognized as safe, it is a frequent cause of allergic contact dermatitis in sensitive individuals. The reaction manifests as redness, itching, and scaling in the underarm area, triggering localized sensitivity.
High concentrations of alcohol, such as ethanol, are common in spray and gel deodorant formulas for quick-drying and antibacterial properties. However, alcohol can be drying to the underarm skin, leading to burning or stinging, especially when applied immediately after shaving. This drying effect compromises the skin barrier and increases irritation.
Another ingredient that frequently causes irritation, particularly in “natural” deodorants, is baking soda (sodium bicarbonate). Baking soda is an effective odor neutralizer because its high alkaline pH creates an environment hostile to odor-causing bacteria. Unfortunately, this high alkalinity can severely disrupt the skin’s naturally acidic protective barrier, leading to a rash, redness, and inflammation for many users.
Selecting Safer Deodorant Options
Making informed choices about underarm products begins with carefully reading the ingredient list, as the product type dictates the presence of aluminum. If avoiding systemic risks like potential endocrine disruptors is a priority, look for products labeled “paraben-free” and “phthalate-free.” Since phthalates can be hidden under “fragrance,” choosing unscented or naturally scented products is a practical strategy to minimize exposure.
If avoiding skin irritation is the goal, seek formulas that use gentler alternatives to common irritants. Instead of baking soda, many sensitive-skin natural deodorants use less abrasive mineral-based ingredients like magnesium hydroxide or zinc ricinoleate to control odor. For those sensitive to propylene glycol, choosing solid stick formulas that use plant-derived oils or butters as a base can help avoid contact dermatitis.
When transitioning from an aluminum-based antiperspirant to an aluminum-free deodorant, a temporary adjustment period is common as the sweat glands regulate. During the first few weeks, a temporary increase in wetness and odor may occur as the ducts clear out. Minimizing irritation involves frequently washing the underarms, ensuring the skin is completely dry before application, and choosing a gentle, non-irritating formula to ease the transition.