Women’s Underarm Odor: Is It Related to Hair-Removal Frequency?

Is underarm odor related to how often someone removes underarm hair? A study of 82 Japanese women found no clear differences in odor intensity according to shaving frequency or previous hair removal at a salon or medical facility. However, greater water loss through the skin was associated with stronger odor.

This 2017 study aimed to compare women’s underarm odor characteristics with men’s and examine relationships with age, earwax type, hair removal, skin condition, and childbirth history. It compared differences among people with their usual habits, rather than experimentally testing the effects of hair removal.

Evaluating 169 women and men 24 hours after washing

The participants were 169 healthy Japanese people recruited in the Kinki region: 82 women in their 20s to 50s and 87 men in their 20s and 40s. Assessments took place in an environmental test room in Osaka in July and August of 2014 and 2015.

For seven days before assessment, participants avoided antiperspirants, deodorants, and fragranced products and used a specified unscented cleanser. They washed their whole bodies about 24 hours before assessment and wore 100% cotton shirts. After 20 minutes in a room at 21°C and 50% relative humidity, a specialist panel of at least four people, including qualified odor assessors, smelled their underarms directly. Right-underarm data were used in the analyses.

Odor intensity was rated from 0 to 5 in 0.5-point steps. Odor quality was described using eight previously established types, including milky, sour, musty, and curry-spice-like. Rather than assigning each person’s odor to a single category, assessors rated the proportions of the different types in 10% steps.

Women’s odor was weaker than that of men of the same age, with a different profile

Mean intensity among participants in their 20s was 2.3 for women and 2.9 for men; among those in their 40s it was 2.1 and 2.6, respectively. Women received lower ratings in both age groups. Men in their 20s had stronger odor than men in their 40s, whereas there was no statistically clear difference across women in their 20s to 50s. These were comparisons between people of different ages, not measurements of aging within the same individuals.

Comparing odor profiles in the 20s and 40s groups, milky odor predominated in both sexes, but made up a larger proportion in women. In men, sour and curry-spice-like notes were prominent after milky notes, whereas these were less prominent in women, particularly the sour component. The authors summarized women’s odor profiles as less diverse than men’s.

Terms such as milky describe what the assessors smelled. The study did not identify the corresponding chemical compounds or bacterial species.

The relationship with earwax differed between women and men

Participants classified their earwax as melted-caramel-like, slightly moist and yellow, or dry. Men reporting caramel-like earwax had stronger underarm odor than the other two groups.

Among women, mean odor intensity was slightly lower in the dry-earwax group, but differences among the three groups were not significant. Some groups were small, so this does not establish that there is no relationship in women. The authors also cautioned against judging women’s underarm odor from earwax type alone.

A relationship with skin water loss rather than hair-removal frequency

Women were classified into frequent shaving (20 participants), intermediate shaving (28), and infrequent shaving (33). Mean odor intensity was 2.3, 2.5, and 2.4, respectively, with no significant difference. Frequent shaving meant almost daily to once every two or three days; infrequent shaving meant once a month or less.

Salon or medical hair-removal history was compared among women in their 20s, where group sizes were relatively balanced: 14 with and 15 without such experience. Both groups had a mean intensity of 2.3. Across all ages, the paper also reported no significant difference between 20 women with and 55 without such experience. The numbers included in shaving-frequency and hair-removal-history analyses differed by question; not every comparison included all 82 women.

Another measurement was transepidermal water loss (TEWL), an indicator of water evaporating through the skin. It was measured after participants washed again following odor assessment and acclimatized for 30 minutes. Across all women, underarm TEWL correlated positively with odor intensity, with a correlation coefficient of 0.40.

When analyzed by earwax group, an association with a coefficient of 0.57 was found in the dry-earwax group, but not a significant one in the other two groups. TEWL also did not differ significantly by shaving frequency or hair-removal history among women in their 20s. The results therefore cannot support the simple explanation that hair removal damages the skin and consequently makes odor stronger.

Childbirth history was also examined, but the mechanism remains unclear

To reduce the influence of age, childbirth history was compared only among women in their 30s: nine who had given birth and seven who had not. Mean odor intensity was 2.8 versus 2.4, a nonsignificant difference. TEWL, however, was higher in those who had given birth, both at the underarm and on the inner upper arm.

The authors discussed possible links between skin condition, bodily changes, and odor. However, menstrual cycle, hormones, and sweat composition were not investigated. What explains the relationship between TEWL and odor, and whether changing TEWL would change odor, remain questions for future research.

The study was limited to participants from the Kinki region assessed in summer, and habits were self-reported. It did not compare the same individuals before and after hair removal, so it cannot establish that hair removal has no effect or justify recommending a particular care method. The authors presented the findings as groundwork for investigating the reasons for sex differences and considering care suited to women.

Summary

The women studied had weaker underarm odor than men of the same age, a larger milky component, and less sour odor. Relationships with age and earwax seen in men did not appear in the same way in women.

Among women, odor intensity did not differ according to shaving frequency or hair-removal history, but greater water loss through the skin was associated with stronger odor. The study shows the importance of considering several aspects, including odor quality and skin condition, rather than hair removal alone when investigating differences in underarm odor.

Research affiliations: All seven authors were affiliated with Mandom at the time of the research. No separate funding or conflict-of-interest declaration was identified.

Reference

Kyuka A, Maeda K, Sawada A, et al. Characteristics of Axillary Odor in the Modern Japanese Female. Journal of Society of Cosmetic Chemists of Japan. 2017;51(2):147–152. doi:10.5107/sccj.51.147