The surprising time you should apply deodorant

There is a key component to better armpit care: know what to apply and when to apply it. Photo / 123rf

The question:

Is it true that you should apply deodorant at bedtime?

The science:

A body odour hack circulating on social media claims that tending to your underarms at night instead of the morning will keep them fresher during the day.

This advice is true, but there is a key component to better armpit care: know what to apply and when to apply it.

Body odour is not caused by sweat alone. Normal skin bacteria break down the sweat into short chain fatty acids, which emit that unpleasant smell. Many people combat the stench with deodorants, antiperspirants or a combination of the two.

Deodorants are intended to mask armpit odour, typically with fragrance, and can be applied anytime and repeatedly throughout the day, such as in the morning, before a workout and after a shower, dermatologists said.

Antiperspirants temporarily block sweat glands, reducing sweat and the resulting body odour. One study reported that participants who used antiperspirants experienced an average sweat reduction of 77.7%. Antiperspirants should be applied to clean, dry skin at bedtime, dermatologists recommend.

“During the night, our body temperature lowers and sweat production decreases, allowing the active ingredients in antiperspirants, typically aluminum-based compounds, to effectively form plugs in the sweat ducts,” said Adam Friedman, a professor and the chair of dermatology at George Washington School of Medicine and Health Sciences. “This process reduces perspiration during the following day.”

Friedman advises his patients to use deodorant in the am and antiperspirant in the pm, he said.

Antiperspirants temporarily block sweat glands, reducing sweat and the resulting body odour. Photo / 123rf

For years, there have been concerns that aluminum-based antiperspirants are linked to Alzheimer’s disease, breast cancer and kidney disease. But much of the current research reports that there is no clear evidence of harm - and those findings have been emphasised by the Alzheimer’s Association, American Cancer Society and National Kidney Foundation.

Because of certain concerns about antiperspirants and kidney disease, however, the Food and Drug Administration, which regulates antiperspirants, requires that they carry a label reading, “Ask a doctor before use if you have kidney disease.”

Friedman and other dermatologists said they have noticed a shift among patients toward aluminum-free antiperspirants, many of which claim to be free of parabens and phthalates too.

Deodorants marketed as natural are not as effective as antiperspirants at reducing excessive sweat and may incorporate ingredients such as fragrances and essential oils that may cause irritation or “allergic contact dermatitis, so it is important to be cautious especially if you have sensitive skin”, said Marisa Garshick, a dermatologist and a clinical assistant professor of dermatology at Weill Cornell Medicine.

Another approach involves targeting the odour-causing skin bacteria so there is less of them to break down the sweat. Some people on social media have opted for antibacterial washes containing benzoyl peroxide or chlorhexidine, products with glycolic acid or straight isopropyl alcohol, all of which “can help with odour, but will not block sweat. They can also be irritating to the skin,” said Shari Lipner, an associate professor of clinical dermatology at Weill Cornell Medicine.

Sticks provide controlled application and more complete coverage. Photo / 123RF

What else you should know:

Choosing a deodorant, antiperspirant or alternative method for underarm odour control is a personal decision, but here are some shopping suggestions from dermatologists:

• Determine what type you need. Deodorants control body odour, and antiperspirants reduce sweating, which then helps to cut down on body odour. Many products include both. “I generally recommend a combined antiperspirant deodorant in a stick format,” Lipner said.
• Decide which formulation works best for you. Sticks provide controlled application and more complete coverage, as do gels and roll-ons, though the latter two often go on wet and need several seconds to dry. Sprays are quick, easy and absorb well, but Garshick noted that some people do not want “to breathe in the aerosol spray” during the application.
• Consider any allergies or sensitivities. People who have sensitive skin may opt for deodorant products without potential irritants such as alcohol, fragrances or certain preservatives, Friedman said. While he does not consider them effective, aluminum-free options with more plant-based ingredients are available, he said.

If you have concerns, such as allergies to certain ingredients, speak with a dermatologist about which product or method would work best for you.

The bottom line:

Antiperspirants, in particular, should be applied at bedtime. When applied at night when sweat production is decreased, the aluminum-based compounds in antiperspirants are better able to plug the sweat ducts to reduce perspiration the next day. Deodorants can be applied at any time.