At a glance
| Chemical family | Unsaturated ketone — secondary product of squalene-ozone chemistry |
| CAS number | 110-93-0 |
| Classification | Not classified by IARC; recognized in indoor air chemistry literature as a marker compound for ozone-skin-lipid reactions; documented respiratory irritant |
| Where you encounter it | Indoor air in occupied rooms; on skin surfaces; on bedding and clothing where skin oils have deposited; in the breathing zone of any room where humans have been present and ozone is infiltrating from outdoors |
| Sleep micro environment relevance | Produced continuously on the bedding and skin surface where ozone (which infiltrates from outdoors even through closed windows) reacts with squalene in skin oils; concentration accumulates overnight in closed sleeping environments; one of the documented characteristic compounds of the SME |
| Activated carbon capture | Moderate — the compound's molecular size and ketone functionality are favorable for activated carbon adsorption; placing the capture medium directly at the skin-bedding interface is the most direct intervention point |
What it is
6-MHO is a methyl ketone with an unsaturated carbon chain — a small molecule by molecular weight (126 g/mol), volatile enough at room temperature to be detected in indoor air, and structurally derived from squalene through a specific oxidation pathway. The compound has a faint citrus or apple-like odor at higher concentrations, though at typical indoor concentrations it is below olfactory threshold.
What makes 6-MHO interesting from a sleep-environment perspective is not what it is — there are many ketones in indoor air — but where it comes from. Squalene is a major component of human sebum, the oil your skin's sebaceous glands secrete continuously. Squalene makes up approximately 10–12% of skin surface lipids. Ozone is a small reactive molecule that exists in outdoor air at concentrations typically in the range of 10–50 ppb and infiltrates through windows, doors, and ventilation into indoor spaces, where it persists at lower but non-zero concentrations of roughly 5–30 ppb.
When ozone encounters squalene on a skin surface or on a bedding surface where skin oil has deposited, it reacts through a chemistry called the Criegee mechanism — a series of ozonolysis steps that break the double bonds in the squalene molecule and produce a cascade of carbonyl compounds. 6-MHO is one of the primary volatile products of this reaction, along with acetone, geranyl acetone, and several aldehydes. Secondary reactions produce further compounds: 4-oxopentanal (4-OPA), 4-methyl-4-oxopentanal (4-MON), and several hydroxycarbonyls.
This chemistry was first thoroughly characterized in a landmark 2010 study by Wisthaler and Weschler, published in the Proceedings of the National Academy of Sciences. Peer-reviewed — Wisthaler & Weschler 2010, PMC2872416 The study established that human skin and skin-oil-contaminated clothing are significant indoor air chemistry sources in their own right — not because they emit pre-existing compounds, but because they host a continuous reaction with ozone that produces compounds that did not exist as separate molecules before the reaction.
How it gets to the bedroom
From your skin, directly
When you are in a room with ozone infiltrating from outdoors, the ozone reacts with squalene on your exposed skin surfaces and produces 6-MHO and other secondary products. These compounds enter the air immediately. A 2024 study published in Environmental Science & Technology measured statistically significant squalene depletion in skin wipe samples after human exposure to 37 ppb ozone — a typical indoor concentration. Peer-reviewed — ACS EST 2024
From bedding where skin oil has deposited
Skin oil transfers continuously from skin to bedding, pajamas, and pillowcases through direct contact during sleep. Once deposited, the skin oil reservoir on these textiles continues to react with infiltrating ozone, producing 6-MHO long after you've gotten out of bed. The 2010 Wisthaler & Weschler study measured ozone deposition velocities of 0.37–0.46 cm/s on skin-oil-soiled cotton, wool, and polyester fabrics — comparable to the deposition velocity on exposed skin itself. Peer-reviewed The bedding is effectively a second skin chemistry-wise: it continues producing 6-MHO 24 hours a day, not just during the hours when you're physically in contact with it.
From the broader Sleep Micro Environment
Multiple peer-reviewed indoor air studies have detected 6-MHO as a characteristic compound elevated during occupied sleep periods, including the 2024 Molinier et al. study that documented 94 compounds substantially elevated in bedroom air during sleep compared to other rooms in the same home. Peer-reviewed — Molinier et al. 2024, PMC11080066 6-MHO is specifically one of the compounds whose presence in the bedroom indicates an active ozone-skin-lipid chemistry happening continuously.
From personal care products that contain squalene or squalane
Cosmetic products containing squalane (the hydrogenated form of squalene, used in many skincare formulations) deposit additional squalene-precursor chemistry onto skin and bedding. The same ozone reaction proceeds, producing the same downstream compounds. People with skincare routines high in squalane have a measurably higher 6-MHO production rate than those who don't, though this contribution has not been quantitatively partitioned from endogenous skin oil contribution.
What the research says
Documented chemistry
The squalene-ozone reaction is one of the best-characterized chemistry pathways in indoor air science. The Wisthaler & Weschler 2010 paper is a foundational reference cited in essentially all subsequent skin-chemistry indoor air work. The 2024 ACS EST paper extended this with controlled human exposure experiments confirming squalene depletion from skin under realistic indoor ozone concentrations. A comprehensive review published in 2022 catalogued the full set of squalene-ozone products and their occurrence in indoor environments. Peer-reviewed — Squalene-ozone review, PMC9231367
Documented health relevance
6-MHO is not classified as carcinogenic and has not been associated with cancer in the published literature. The compound is, however, a respiratory irritant at concentrations that occur in indoor environments. Peer-reviewed Some of the secondary products of the same chemistry — particularly 4-OPA and other dicarbonyls — are more reactive and have stronger biological effects than 6-MHO itself. The downstream secondary chemistry is therefore part of the relevance, not just the compound that gets measured.
What this chemistry implies for the broader picture
The most important thing the 6-MHO research has established is structural rather than specific: a meaningful portion of the chemistry in a closed bedroom during sleep is not coming from the mattress, the cleaning products, or anything that was manufactured separately and brought in. It's being produced by the interaction between the occupant's own skin lipids and an atmospheric trace gas that exists everywhere on Earth. This means "removing the contamination" from a bedroom is conceptually more like the way a kitchen handles cooking emissions — there's an active, continuous process producing the relevant chemistry — than the way a closet handles stored materials. The intervention point is at the source surface (skin or bedding) or in the breathing zone immediately above it, not in the room as a whole. Inferred from the documented chemistry
This is also the chemistry that demonstrates most clearly why a single-villain framing of "what the mattress is off-gassing" misses substantial portions of the bedroom chemistry picture. The mattress matters. Body chemistry matters. The interaction between the two — and between both and infiltrating ozone — is the actual subject of bedroom chemistry research.
What helps reduce exposure
Wash bedding frequently. Skin-oil-deposited bedding is a continuous 6-MHO production surface. Weekly or more frequent washing reduces the squalene reservoir on which the ozone chemistry runs. This is the lowest-cost, most direct intervention point for this specific compound. Peer-reviewed
Shower before bed. Showering removes a substantial fraction of accumulated squalene from skin surfaces. The morning-shower vs. evening-shower question has different answers for different reasons — but for ozone-skin chemistry specifically, washing skin before sleep reduces the squalene available for ozone to react with during the sleep window.
Reduce indoor ozone. Ozone infiltrates from outdoors. On high-ozone days (typically summer, sunny afternoons in urban areas), closing windows during peak outdoor ozone periods and opening them at night when outdoor ozone is lower reduces the indoor concentration available for skin reactions. Activated carbon air purification removes ozone effectively. Indoor ozone-generating air purifiers — devices marketed as "ionic" or "ozone-generating" — actively make this chemistry worse and should be removed from any bedroom where someone sleeps.
Choose cotton or wool sheets over synthetics for ozone-chemistry reasons. Skin oil deposits more readily on cotton and wool than on synthetic fabrics, but cotton and wool are also more readily washable and more frequently washed. The net effect is that natural fibers, when laundered regularly, may produce less accumulated squalene-ozone chemistry than synthetics that are washed less often. This is inference from the documented deposition kinetics rather than a direct comparison study. Inferred
For activated carbon at the sleep surface: capture at the source. This is the most direct chemistry-based application of an activated-carbon sleep layer. A medium that intercepts the volatile products of skin-ozone chemistry between the skin/bedding surface and the breathing zone reduces inhalation exposure without requiring the skin chemistry itself to stop happening. The capture is at the right point in the system. This is one of the chamber-test protocols Embr's research program is designed to evaluate. Speculation — the broader activated-carbon-ketone adsorption chemistry is documented; the sleep-surface application has not been measured
What does NOT help
- Air purifiers without ozone-removal capability. Many residential air purifiers reduce particles but pass ozone through unchanged or, in some cases, generate ozone as a byproduct. The label "ionizer" or "plasma" generally indicates a unit that either produces or fails to remove ozone. For squalene-ozone chemistry specifically, the relevant filter capability is ozone removal, not particle filtration.
- Citrus-scented cleaning products or air fresheners. These contain limonene, which reacts with ozone to produce its own set of secondary products including formaldehyde. Adding more terpene chemistry to a bedroom that already has skin-ozone chemistry running compounds rather than relieves the issue. Peer-reviewed
- Sealing the room. Reducing ventilation reduces ozone infiltration in one sense, but also concentrates the chemistry products that have already formed. The net effect on 6-MHO concentration depends on the balance between reduced ozone input and reduced product removal, and the modeling shows it varies by specific room characteristics. Fresh-air ventilation is generally still beneficial for breathing-zone air quality even though it increases ozone input.
Open research questions
- The relative contribution of skin-ozone chemistry versus mattress off-gassing versus other indoor air sources to the total sleep-environment exposure profile for the documented secondary chemistry products (6-MHO, 4-OPA, geranyl acetone, and others). Speculation — the individual chemistries are documented; the integrated bedroom-level partitioning has not been published
- The capture efficiency of activated carbon fiber cloth at the sleep-surface interface for 6-MHO and its secondary products under body-heat and body-pressure conditions. Speculation
- Whether dietary squalene intake or topical squalane-containing skincare meaningfully changes the rate or product spectrum of skin-ozone chemistry. Speculation — the mechanism would exist; the dose-response has not been studied
- Whether population-level differences in skin oil composition (across age, sex, ethnicity, diet) produce population-level differences in skin-ozone chemistry output. Speculation
Citations
- Wisthaler A, Weschler CJ (2010). Reactions of ozone with human skin lipids: Sources of carbonyls, dicarbonyls, and hydroxycarbonyls in indoor air. Proceedings of the National Academy of Sciences 107(15):6568–6575. PMC2872416 Peer-reviewed — landmark study
- Reactions and Products of Squalene and Ozone: A Review (2022). PMC9231367 Peer-reviewed — comprehensive review
- Squalene Depletion in Skin Following Human Exposure to Ozone (2024). Environmental Science & Technology. DOI 10.1021/acs.est.3c09394 Peer-reviewed
- Molinier B, Arata C, Katz EF, Lunderberg DM, Ofodile J, Singer BC, Nazaroff WW, Goldstein AH (2024). Bedroom Concentrations and Emissions of Volatile Organic Compounds during Sleep. Environmental Science & Technology 58(18):7958–7967. PMC11080066 Peer-reviewed
- Weschler CJ, Nazaroff WW (2005). Workgroup Report: Indoor Chemistry and Health. Environmental Health Perspectives. PMC1392240 Peer-reviewed
- Weschler CJ (2018). Indoor Chemistry. Environmental Science & Technology. DOI 10.1021/acs.est.7b06387 Peer-reviewed
Frequently asked questions
-
What is 6-MHO and why is it in my bedroom?
6-MHO is a small ketone produced when ozone — a reactive trace gas that infiltrates indoor air from outdoors — reacts with squalene, a major component of human skin oil. The reaction happens continuously on the surface of exposed skin and on bedding where skin oils have deposited. It's in your bedroom because your own body produces the precursor, and the reaction completes the chemistry in the presence of ozone. This is a documented indoor chemistry pathway, not a contamination source from outside your body. Peer-reviewed
-
Is 6-MHO dangerous?
6-MHO is not classified as carcinogenic and has not been associated with cancer or other major chronic disease outcomes in the published literature. The compound is a respiratory irritant at higher concentrations, and some of the downstream secondary products of the same chemistry (4-OPA in particular) are more reactive. The honest answer is that the health effects of chronic low-level exposure to the full mix of squalene-ozone products are an active area of research rather than a settled question. Peer-reviewed for individual compound classifications; Speculation for the full mix's health implications
-
Why isn't this in most consumer writing about bedroom chemistry?
Because the consumer category has been organized around products and what's wrong with them, not around the chemistry of the room as a system. The mattress, the cover, the flame retardants — these are products with manufacturers and supply chains, which makes them legible to the consumer-protection framing. The chemistry your own body is producing has no manufacturer to point at, no recall to issue, no certification to design. It just happens. Most consumer publications focus on the parts of the picture that can be solved through purchasing decisions, not the parts that require understanding the chemistry as a system.
-
Does an air purifier remove 6-MHO?
Activated carbon air purifiers reduce 6-MHO concentrations. HEPA-only filtration does not. The more important upstream intervention is ozone removal — if you reduce the ozone that drives the reaction, you reduce the production rate of 6-MHO and all the related products. Activated carbon air purifiers rated for ozone removal are the right product category for this chemistry. Peer-reviewed
-
Can I reduce 6-MHO production by changing my diet or skincare?
Possibly, but the evidence is thin. Squalene is produced endogenously by your sebaceous glands and the production rate varies with age, sex, hormone levels, and individual variation more than with diet. Topical squalane (the hydrogenated form used in some skincare products) adds to the surface squalene pool and increases the substrate for ozone chemistry. Reducing leave-on products containing squalane before bed is one direct intervention. The diet-skincare-chemistry relationship is an underexplored research area. Inferred from mechanism; not directly studied
Related compounds
Embr Sleep is a sleep environment company researching and addressing the chemistry of the bedroom — including the chemistry that the bedroom itself produces from the interaction between occupant body chemistry and atmospheric trace gases. Our work on skin-ozone chemistry products focuses on capture at the sleep-surface interface, where the compounds are produced. This work is in research and product development.
Last reviewed 2026-05-15. If you find a factual error, contact us.