The answer lies in the pronounced inter- and intra-individual variability of reproductive hormones. Calendar calculations, basal body temperature monitoring, and urine strip tests are widely used, but they are limited by short-lived hormonal peaks, variability between women, and susceptibility to confounding factors. Breath VOCs, which reflect systemic metabolism and can be measured non-invasively and in real time, may offer a complementary window on the physiological state of the cycle.

The menstrual cycle is accompanied by coordinated endocrine and metabolic responses well beyond the reproductive tract. Basal body temperature, breast volume, insulin sensitivity, and end-tidal carbon dioxide concentrations all fluctuate across the follicular and luteal phases. Prior work has suggested that breath profiles of acetone, isoprene, and sulfur-containing compounds may vary across the cycle and around ovulation.

Yet only a limited number of studies have tracked longitudinal changes in breath VOC profiles throughout a natural cycle, and the relationship between breath signals and circulating reproductive hormone concentrations has remained unclear. The new pilot study was designed to probe exactly that gap. Technically, the approach relies on PTR-TOF–MS, an instrument that ionizes trace gases in exhaled breath using hydronium reagent ions and then separates the resulting product ions by their exact mass-to-charge ratios with time-of-flight mass analysis.

In this configuration, the drift tube was operated at 80 degrees Celsius and 2.6 mbar pressure with a drift voltage of 561 V and an electric field strength of 120 Townsend, and the acetone product ion at m/z 59.05 was monitored during exhalation to determine end-tidal points, ensuring that samples reflected alveolar air rather than dead-space gas. The method allows real-time, non-invasive measurement of many signals simultaneously, each reported according to its m/z value with tentative compound assignments drawn from a PTR library. Recruitment was careful and deliberately restrictive.

Ten women with regular menstrual cycles were enrolled; all were healthy non-smokers, not using hormonal contraception or medication, and fasting at the time of sampling. Breath and blood samples were collected on two days in the follicular phase (preovulatory days 0 to 12), on the day of ovulation, and on two days during the mid-luteal phase (postovulatory days 16 to 21). Ovulation was determined by serum luteinizing hormone (LH), estradiol (E2), and progesterone (P) levels, with predefined cut-offs: LH either doubling from baseline or exceeding 10 IU/L, E2 above 100 pg/mL as an indicator of follicular development, and P above 4.5 ng/mL indicating luteinization.

Ovulation was subsequently confirmed through a retrospectively obtained menstrual history. Of the ten recruited women, only five entered the final analysis. Two participants were excluded because their breath measurements had been performed on a different PTR-TOF–MS instrument, a decision made to circumvent any potential cross-instrument variability.

Three more were excluded because fever and/or antibiotic treatment could substantially alter breath VOC profiles and confound the assessment of cycle-related changes. The exclusions, while necessary for data integrity, underscore a recurring challenge in breath research: environmental and behavioral influences, from diet and co-medication to sampling conditions, can shape the VOC composition of exhaled air even under standardized protocols. The statistical picture that emerged was phase-dependent but selective.

Comparing breath VOCs among the follicular, ovulatory, and luteal phases showed trends toward phase-dependent differences for the signals at m/z 41.04 (p = 0.050), m/z 67.05 (p = 0.099), and m/z 69.07 (p = 0.166). When the analysis narrowed to ovulatory versus non-ovulatory measurements, the signal at m/z 41.04 was significantly higher during ovulation (p = 0.021). Median signal intensities were 24,567 (interquartile range 20,851 to 26,962) during ovulatory measurements and 15,480 (13,179 to 16,992) during non-ovulatory measurements, a substantial relative difference for a single ion signal.

In contrast, m/z 67.05 and m/z 69.07 did not reach statistical significance in the ovulatory comparison (both p = 0.064). Just as telling was what did not appear. No significant correlations were observed between any breath VOC signals and serum concentrations of LH, E2, or P, although positive trends were noted between E2 and the signals at m/z 41.04 (Spearman's rho = 0.448, p = 0.145) and m/z 67.05 (rho = 0.497, p = 0.101).

The authors interpret this absence cautiously. In PTR-TOF–MS, the hydrocarbon-related fragment ions at m/z 41.04 and m/z 67.05 are associated with lipid- or isoprene-related metabolism rather than individual compounds, and reporting m/z features rather than fully identified molecules is common practice in exploratory PTR-TOF–MS studies, particularly when signals show reproducible physiological associations. The metabolic backdrop may explain why breath signals lag behind hormone peaks.

Lipid and lipoprotein levels and oxidative stress are known to fluctuate during the menstrual cycle. Mumford and colleagues observed that lipoprotein cholesterol levels vary in response to changing estrogen levels, with low-density lipoprotein cholesterol highest during the follicular phase and high-density lipoprotein cholesterol highest around ovulation. High E2 concentrations during the follicular phase have been shown to have antioxidant properties, while fluctuations of liver enzymes during the normal cycle are possibly mediated by progesterone.

Ovulation itself is associated with profound metabolic and endocrine changes, including increased steroidogenesis, altered lipid turnover, and shifts in oxidative metabolism. Whether lipid peroxidation or oxidative stress-related processes influence specific ion signals, such as ethane- or pentane-related features, in breath remains unresolved. The authors suggest that metabolic markers may not follow the rapid and phase-specific secretion patterns of reproductive hormones, but rather integrate hormonal effects over time, providing complementary information on the physiological state.

The authors are explicit that these findings should be regarded as hypothesis-generating rather than definitive. The main limitations are the small sample size and the exploratory design. Breath VOCs remain susceptible to environmental and behavioral influences despite standardized sampling, and even exhaled isoprene, produced in the muscles, changes rapidly with variations in physical activity and may be influenced by minimal movements during sampling.

The authors note that larger studies with higher temporal resolution and independent validation cohorts should account for confounders such as circadian rhythms, exogenous contaminants, and humidity, and that mixed-effects or generalized estimating equation models would have been appropriate for the repeated-measures structure. No formal correction for multiple comparisons was applied, because stringent correction on a small pilot cohort would substantially increase the risk of Type II errors, and post-hoc power and minimum detectable effect analyses were not conducted. The possibility of selection bias could not be discounted.

What the study does establish is a proof of concept with a clear mechanistic framing. Breath VOCs exhibit phase-dependent alterations across the menstrual cycle, and the observed increase in the m/z 41.04 signal during ovulation may reflect integrated metabolic adaptations associated with endocrine changes rather than direct surrogates of circulating hormone concentrations. In other words, breath chemistry may not mirror the rapid, phase-specific secretion patterns of reproductive hormones; instead, it may integrate hormonal effects over time, providing complementary information on the physiological state that conventional ovulation tests may miss.

The authors frame the results as requiring confirmation in larger prospective studies, positioning breath analysis not as a replacement for hormone-based methods but as a potential adjunct capturing the systemic metabolic consequences of the endocrine events driving ovulation. For now, the signal at m/z 41.04 stands as a promising, unconfirmed lead in a field where the breath may yet speak where hormones fall silent.

Subject of Research: Breath volatile organic compounds across the menstrual cycle measured by PTR-TOF–MS

Article Title: Breath Volatile Organic Compounds Across the Menstrual Cycle: A Pilot Study Using PTR-TOF–MS

Article References: Eckhardt, C., Lederer, W., Wildt, L., Böttcher, B., & Ruzsanyi, V. (2026). Breath Volatile Organic Compounds Across the Menstrual Cycle: A Pilot Study Using PTR-TOF–MS. Reproductive Sciences. https://doi.org/10.1007/s43032-026-02249-7

Image Credits: AI Generated

DOI: 10.1007/s43032-026-02249-7

Keywords: breath analysis, volatile organic compounds, menstrual cycle, ovulation, PTR-TOF-MS, mass spectrometry, reproductive endocrinology, estradiol, luteinizing hormone, progesterone, isoprene, pilot study

The experimental design is deceptively simple but methodologically deliberate. Stage 1 held ghee at 60 to 70 degrees Celsius for 30 minutes in a water bath, mimicking warm storage and culinary preheat. Stage 2 ramped the sample from 220 to 340 degrees Celsius in 20-degree steps, each held for five minutes, under flowing nitrogen to suppress oxidative side reactions. Stage 3 dropped the sample directly into a muffle furnace set to a nominal 500 degrees Celsius for just 90 seconds, a condition meant to model the pyrolytic shock of a cooking flare-up rather than ordinary frying. The authors are candid about a key caveat here: no thermocouple sat at the sample, and a 50-gram liquid charge cannot reach furnace temperature in 90 seconds, so the reported set point is an upper bound on what the ghee actually experienced. Five independent replicates were run for each stage and each temperature step, giving the statistical backbone for the comparisons that followed.

At the gentle end of the scale, the chemistry was quiet but measurable. Infrared spectroscopy of the residue showed a broadening O-H stretch and a growing carbonyl feature, the fingerprints of ester hydrolysis, the slow cleavage of the fat’s triglyceride bonds by water. Titration confirmed it: free fatty acid content rose from 0.42 percent to 0.71 percent over the 30-minute hold, a statistically significant increase, while free glycerol, released from the same broken esters, accumulated to 0.18 percent of sample mass. Crucially, no volatile carbonyls escaped at this temperature. Glycerol was liberated but not yet dehydrated, meaning the fat was ageing without yet becoming a source of airborne toxins. The team notes this mirrors the mild hydrolytic ageing documented in butter during warm storage, and that the two-step cascade they propose, hydrolysis first and dehydration later, remains plausible but unproven because the stages used separate aliquots of ghee.

The intermediate stage is where the story turns toxic. As the temperature climbed through the 280 to 320 degrees Celsius window, acrolein, a pungent, irritating aldehyde flagged by food scientists and air-quality regulators alike, surged to a maximum of 112.6 micrograms per gram of ghee at 300 degrees Celsius, accounting for 64.2 percent of all carbonyls detected by derivatisation and high-performance liquid chromatography. Above 300 degrees the acrolein yield fell, consistent with the molecule itself breaking apart into smaller fragments. The peak sits squarely inside the 280 to 340 degrees Celsius window known for catalytic glycerol dehydration, and the glycerol backbone of triglycerides, not the fatty-acid chains, is the established precursor. In other words, the glycerol freed during low-temperature hydrolysis becomes the feedstock for acrolein once the ghee approaches its smoke point, a two-act mechanism the data support circumstantially if not yet causally.

Stage 3 delivered the study’s most tantalising puzzle. Within a minute of insertion into the hot furnace, the headspace flooded with volatile fragments, and proton-transfer-reaction time-of-flight mass spectrometry caught a base peak at nominal mass-to-charge ratio 27 that rose between 45 and 60 seconds and decayed to background by about 180 seconds, with a 1/e decay time of 90 to 140 seconds. The signal matched none of the carbonyl reference standards. The team systematically eliminated the obvious candidates: vinyl alcohol, ketene and propene would all appear at different masses in proton-transfer ionisation, and the absence of any protonated parent at mass 43 rules out ketene and propene outright. The falling intensity across masses 27, 28 and 29 suggests hard, electron-impact-like fragmentation rather than soft proton transfer. Definitive identification would have required exact-mass measurement to distinguish the C2H3+ ion at 27.0229 from other formulas, but the raw high-resolution data files were not retained and cannot be recovered. The researchers therefore report an unassigned transient ion, an unusually honest label in a field where over-claiming is common.

Conventional bag sampling told a complementary story. Tedlar-bag gas chromatography-mass spectrometry of the Stage 3 headspace detected acrolein at 245 micrograms per gram, along with benzene, toluene, 1,3-butadiene and 2-methylfuran, a roster of light aromatics and dienes consistent with radical cracking of fatty-acid chains above 400 degrees Celsius. Notably, the transient mass-27 ion was absent from the bag samples, consistent with a lifetime shorter than the storage interval, exactly the class of short-lived reactive species that conventional cooking-emission studies, which typically operate at 150 to 250 degrees Celsius and rely on bag capture, have never catalogued. Mass-balance accounting showed progressive loss of material through the stages, with the lowest recovery at Stage 3, the missing fraction inferred to be non-condensable gases such as hydrogen, methane and carbon monoxide that the protocol did not capture.

The most unexpected experiment came last. The team injected 100 millilitres of pyrolysis gas into a 2.5-litre humid chamber held at 25 degrees Celsius and 65 percent relative humidity, alongside blank and nitrogen-injection controls, and watched what happened to the water. Gravimetric uptake on desiccant cartridges reached 1.3 milligrams after 30 minutes in the pyrolysis condition, against 0.3 milligrams for the blank and 0.4 for the nitrogen control, a difference that held up statistically against the blank and was marginal against the nitrogen control. Raman spectroscopy of the chamber’s O-H stretching envelope told the same story from a different angle: under pyrolysis gas the envelope maximum shifted 4 to 7 wavenumbers toward lower frequency, and roughly 8 percentage points of intensity migrated from the higher-frequency sub-band to the lower-frequency one, a redistribution consistent with oxygenated organic species hydrogen-bonding to water.

The authors are careful, almost to a fault, about what this chamber result does and does not mean. The Raman envelope peaks near 3400 wavenumbers, the signature of condensed water, not the two narrow gas-phase stretches near 3657 and 3756, so the signal reflects an integrated chamber water response dominated by condensed films and droplets rather than resolved gas-phase clusters. The 100-millilitre injection is a 4 percent by-volume perturbation, several orders of magnitude above ambient cooking-VOC mixing ratios, and with only three replicates per condition the design detects only large effects. The team explicitly frames the experiment as a laboratory feasibility observation carrying no atmospheric inference. Still, the coincidence of gravimetric uptake, spectral shift and sub-band redistribution is a genuine first: no prior study has tested whether high-temperature lipid pyrolysis products perturb a water-vapour hydrogen-bonding network at all, and the answer, provisionally, is that they do something measurable.

The practical implications reach from the stovetop to the atmosphere. Cooking is a newly recognised heavyweight in urban air chemistry, accounting for up to 20 percent of anthropogenic volatile organic compound emissions in some PTR-MS field studies, with cooking organic aerosol emission factors spanning 0.1 to 6 grams per kilogram of food. In domestic cooking, where temperatures rarely exceed 250 degrees Celsius, the study suggests the acrolein window opens as ghee nears its smoke point, reinforcing long-standing concerns about overheating clarified butter. The Stage 3 regime applies only to flare-ups, oil fires and industrial high-heat frying, but it is precisely there that short-lived reactive species, the kind no bag sample can catch, are released. The authors lay out a clear roadmap: a continuous temperature ramp tracking free fatty acid, glycerol and acrolein simultaneously to confirm the hydrolysis-dehydration cascade; high-resolution mass spectrometry with isotope-pattern resolution to finally name the mass-27 ion; and chamber experiments at parts-per-billion mixing ratios with condensed water controlled, ideally in vessels above 100 litres with cryogenic trapping. Until then, the humble jar of ghee carries a chemical secret that only extreme heat, and now careful instrumentation, can reveal.

Subject of Research: Thermal degradation chemistry of cow ghee from hydrolysis to pyrolysis and its pyrolysis products' interaction with water vapour

Article Title: Thermal decomposition of cow ghee by multi-stage heating and preliminary study of interactions of pyrolysis products with water vapour

Article References: Dorepalli, N. R., Prasad, M. S. V. K. V., & Pappoppula, S. (2026). Thermal decomposition of cow ghee by multi-stage heating and preliminary study of interactions of pyrolysis products with water vapour. Discover Chemistry, 3(1), Article 564. https://doi.org/10.1007/s44371-026-01008-6

Image Credits: AI Generated

DOI: 10.1007/s44371-026-01008-6

Keywords: cow ghee, acrolein, pyrolysis, glycerol dehydration, PTR-ToF-MS, FTIR, HPLC-DNPH, cooking emissions, indoor air quality, water vapour, Raman spectroscopy, free fatty acids