Does Shaving Help Washing Reduce Underarm Odor?

Trimming underarm hair, shaving it, or removing it with wax: do all these methods change odor after washing in the same way?

In a study of 30 men, shaving or waxing followed by washing with soap produced larger immediate reductions in odor ratings than washing alone. By contrast, trimming with scissors showed no clear additional benefit immediately after the first wash. The differences depended not simply on whether hair was removed, but on how it was removed and how much time had passed since washing.

Does hair removal change how effectively washing reduces odor?

Lanzalaco and colleagues’ paper was published online in 2015 and appeared in a 2016 journal issue. It aimed to compare, under defined conditions, how much different underarm hair-removal methods helped soap washing reduce odor in men. The researchers followed not only the initial change but also the return of odor and the effects of washing again on subsequent days.

Participants were White men aged 18–48 who had a minimum level of underarm odor at screening and no excessively large difference between underarms. People with skin irritation, infection, or other exclusion conditions were not included. All 30 participants completed the trial.

Assigning two of four treatments to each person’s two underarms

The four conditions were washing with hair left intact, clipping close to the skin with scissors followed by washing, shaving followed by washing, and waxing followed by washing. Each person did not undergo all four conditions; instead, two different conditions were randomly assigned to their left and right underarms. Each condition was evaluated in 15 underarms.

Participants avoided underarm deodorants, antiperspirants, fragranced products, and similar products throughout a 14-day preparation period and the trial. Before baseline measurements, they washed with a 2% unscented soap solution, and odor was assessed 24 hours later.

In the main trial after hair removal, all conditions involved washing with a 10% unscented soap solution. Washing was standardized to 10 seconds, followed by 20 seconds of rinsing with warm water. The same 10% solution was used for washing on the next two days.

The shaving procedure included clipping first and lathering with soap before shaving. Waxing included wiping afterward with a cold, wet towel. Thus, the comparison was between combinations of practical procedures, not a comparison that changed only the presence or absence of hair.

Four trained assessors smell directly at successive time points

Four trained assessors smelled the underarms through a cup-shaped device placed against the underarm and rated odor on an 11-point scale from 0 to 10. They were not told the treatment assignments or previous ratings, but the underarms remained visible, leaving room for expectations based on hair condition to influence assessment.

On the first day, ratings were taken immediately after treatment and washing, then 12 and 24 hours later. Participants washed again on each of the following two days, with ratings immediately after washing and 24 hours afterward. Hair removal itself was performed only once, on the first day.

The analysis accounted for baseline odor, side, and differences between participants. The paper adopted p < .10 as its significance threshold, a less stringent criterion than the commonly used p < .05. This matters particularly when interpreting the 24-hour findings.

Larger immediate reductions after the first wash with shaving and waxing

The mean reduction in odor ratings from baseline was 23.5% with washing alone and 27.2% with clipping followed by washing. There was no clear difference between these two conditions.

Washing after shaving reduced ratings by 57.3%, and washing after waxing by 75.3%. Both reductions were larger than with washing alone, with p < .0001 in each case. This immediate post-treatment difference was the clearest finding.

These percentages were calculated as changes in odor ratings relative to baseline. They do not mean that odor molecules decreased by 57% or bacteria by 75%. What was actually measured was odor intensity as perceived by the assessors.

Persistence over 24 hours and washing again the next day are different findings

With time, none of the conditions retained reductions as large as those seen immediately after the first wash. At 24 hours, the reduction was 14.6% in the shaving condition and 6.2% with washing alone, but the p value for this difference was .0682. Although it met the paper’s 10% criterion, it did not meet the conventional 5% threshold, so a strong claim that the effect reliably lasts 24 hours would require caution. Differences for waxing and clipping at 24 hours were not clear even under the paper’s criterion.

When participants washed again the next day, however, the immediate reductions were 25.0% with washing alone, 45.2% in previously shaved underarms, and 54.7% in previously waxed underarms. Immediately after washing on the following day, shaving and waxing also yielded lower odor ratings than washing alone. Clipping produced a 35.6% reduction immediately after washing on the second day, a significant difference from washing alone, but not a clear difference on the first or third day.

In other words, after a single hair-removal procedure, subsequent washing also tended to reduce odor more effectively immediately afterward. However, 24 hours after those washes, ratings in each condition had returned close to baseline. This should not be interpreted as odor remaining low continuously for several days.

Why washing became more effective remains a hypothesis

The authors suggested that shaving or plucking hair could help cleansers reach the skin and follicular openings, making secretions easier to remove. Removal of surface skin cells or sebum during treatment may also have contributed.

However, this trial did not measure bacterial numbers or types, sweat volume, or odor molecules. The paper itself identified whether bacterial reduction occurred as a question for further study. The limited initial benefit of clipping alone also suggests that the skin treatment and washing procedure need to be considered alongside hair length.

No adverse events were reported during the trial, but participants reported considerable discomfort during waxing. The sample was also limited to 30 men meeting particular criteria, so the findings provide only limited grounds for recommending the same methods broadly to people with different skin characteristics or usual product use.

Summary

Under these conditions, soap washing after shaving or waxing produced larger immediate reductions in underarm odor ratings than washing alone. Differences were also seen immediately after washing on the next two days, whereas clipping alone offered no clear additional benefit after the first wash.

Odor returned with time, and the difference 24 hours after shaving was not significant at the conventional 5% threshold. Rather than showing that hair removal prevents odor for days, the study shows more specifically that the removal method affects the reduction in odor immediately after washing.

Procter & Gamble funded the clinical trial and support for preparation of the paper. All authors disclosed that they were employees of the company. These statements refer to their affiliations at the time of the research.

Reference

Lanzalaco A, et al. A comparative clinical study of different hair removal procedures and their impact on axillary odor reduction in men. Journal of Cosmetic Dermatology. 2016;15(1):58–65. doi:10.1111/jocd.12197. Open-access full paper.