Evidence: the studies behind Phiome

Registered trial

Design: Randomised and placebo-controlled. Each participant used the bacterial spray for one month and a placebo spray for one month. The participants, care providers and odour panel did not know which spray was used.
Participants: 67, Ghent University, 2018 to 2020
Measured: Underarm bacteria (DNA analysis), odour molecules (GC-MS) and odour panel assessments
Result: Underarm odour improved, and became less intense. Odour panel assessments and GC-MS results still showed the improvement after people stopped using the spray.
Bacteria: Odour-causing bacteria such as Corynebacterium, Anaerococcus, Peptoniphilus, Moraxella and Campylobacter decreased. Neutral-smelling Staphylococcus increased.
Odour molecules: Significantly fewer of the molecules related to musty and faecal odour, such as naphthalene and indole, and related to sour and sulphurous odour, such as 2-propenoic acid methyl ester, mid-chain fatty acids and sulfonylbismethane.
Status: Completed
Source: ClinicalTrials.gov, NCT03967470

Pilot

Design: Armpit bacterial transplants. Bacteria from a family member with little odour were applied to the armpit of a person with a strong smell, after a week of thorough washing.
Participants: 18 participants
Result: Odour improved for at least a month. The effect could fade after a few months, which led to the idea of a spray.
Status: The approach is described in a viewpoint article.
Source: Experimental Dermatology, 2017

Peer-reviewed

Design: Nine volunteers stopped or started using deodorant or antiperspirant for one month. Swabs before, during and after.
Measured: Underarm bacteria (DNA analysis)
Result: Deodorants and antiperspirants shifted the armpit microbiome. Antiperspirants had the biggest impact, and shifted it towards more odour-causing bacteria.
Source: Archives of Dermatological Research, 2014

Peer-reviewed

Design: Volunteers used an antiperspirant, a foot powder, a moisturiser and a sunscreen. Skin bacteria and skin chemistry were measured before, during and after.
Result: Antiperspirants shifted the armpit microbiome towards more resistant, Gram-negative bacteria, and increased bacterial and chemical diversity, not for the better. The more antibacterial ingredients a product contains, the bigger its impact on the skin microbiome.
Source: BMC Biology, 2019

Peer-reviewed

Design: Armpit samples from 53 healthy people, some followed over time
Measured: Underarm bacteria (DNA analysis)
Result: Staphylococci and corynebacteria dominated. Women mostly had staphylococci, men more often corynebacteria. Each armpit was unique, and fairly stable over time.
Source: PLoS ONE, 2013

Peer-reviewed

Design: Shirts from 26 people after an hour-long spinning session, smelled by a trained odour panel
Result: Polyester smelled worse than cotton. Micrococci, bacteria that turn sweat into odour, grew better on polyester. Each type of textile fibre enriches or suppresses specific bacteria.
Source: Applied and Environmental Microbiology, 2014

Peer-reviewed

Design: Five households. A new piece of cotton was washed with regular laundry at 30 °C, with a detergent without bleach.
Result: Bacteria from skin and clothes ended up on the clean cotton. The rinse water still held up to millions of living bacteria per millilitre.
Source: Frontiers in Microbiology, 2015

Peer-reviewed

Design: Clothes and washing machines from 31 households, analysed with DNA sequencing (shotgun and 16S), flow cytometry, odour assessments and GC-MS olfactometry.
Result: Laundering increased the number of living bacteria on clothes, led to more biofilm formation and to more potentially harmful bacteria. Drying clothes in humid conditions made it worse.
Source: BMC Biology, 2025

Review

Summary: Many skin conditions go together with an imbalance in the skin microbiome. This review compares the ways to change it: transplanting a whole community of skin bacteria, applying selected strains (bacteriotherapy), and using pre-, pro- and postbiotics, with the clinical trials so far for common skin conditions.
Conclusion: Both whole-community transplants and single strains have shown benefits. The skin microbiome is a promising route for new treatments and cosmetics.
Source: Computational and Structural Biotechnology Journal, 2021

What we tested, and where it stands.