The bottom line first.
On May 21, 2026, Japan’s Ministry of Health, Labour and Welfare (MHLW) released a comprehensive evaluation on the health effects of heated tobacco products (HTPs). It is the first formal review by a Japanese government body, drawing on domestic and international literature published between 2010 and 2025. The findings give neither side of the HTP debate a clean win — they deliver three sobering conclusions.
- Conclusion 1: Indoor air clearly becomes contaminated (strong evidence)
- Conclusion 2: Respiratory effects on bystanders are “suggested” (moderate evidence)
- Conclusion 3: Carcinogenicity, effects on pregnant women, and effects on children are “not yet determinable” (insufficient data)
Japan has the world’s highest HTP adoption rate, with roughly 11% of adults — about 11 million people — using these devices. Many switched from cigarettes believing HTPs were “safer.” The MHLW review neither endorses nor refutes that belief. That’s exactly why understanding it correctly matters.
💡 This article is not medical advice. Always consult your physician about smoking, quitting, or tobacco product choices.
What happened — the May 21 announcement
The release came from the Tobacco Health Impact Evaluation Committee under MHLW’s Council on Health Sciences. At the May 21 meeting, the research panel presented an evaluation document summarizing 15 years of published literature.
Three features make this evaluation important:
- Long time horizon: 2010–2025 (15 years). Covers virtually all post-2014 papers, the period when HTPs entered Japan
- Includes both manufacturer-funded and independent research from Japan and abroad
- Item-by-item assessment rather than a single verdict — air quality, respiratory effects, carcinogenicity, and effects on pregnant women / children are evaluated separately
The committee will use this evaluation to determine regulatory direction by year-end. This directly feeds into the ongoing debate around amending Japan’s Health Promotion Act.
Conclusion 1: Indoor air clearly becomes contaminated (strong evidence)
The most clearly established finding is that HTP use increases harmful substances in the surrounding air.
Specifically, the following substances have been detected in air around HTP users:
- Nicotine (some products release concentrations comparable to combustible cigarettes)
- Aldehydes (formaldehyde, acetaldehyde, and others)
- Volatile organic compounds (VOCs)
- Ultrafine particles (below PM2.5 size range)
Emissions are lower than combustible cigarettes — but the panel repeatedly confirmed they are not zero. When used indoors, non-smokers in the same room inhale these substances.
“You can’t see smoke, so it must be safe.” “It doesn’t smell, so it’s harmless.” Both are wrong. The vapor is invisible and odorless, but the air is genuinely contaminated.
Conclusion 2: Respiratory effects on bystanders are “suggested” (moderate evidence)
The evaluation describes the link between secondhand HTP exposure and respiratory symptoms (cough, phlegm, shortness of breath, asthma exacerbation) as “effects are suggested.”
“Suggested” is researcher-speak for a careful middle ground. The nuance translates as follows:
| Wording | What it means |
|---|---|
| “A strong association is recognized” | Causation is virtually confirmed |
| “Effects are suggested” | Multiple studies show an association, but proof is still incomplete |
| “Cannot be determined” | The data itself is insufficient |
In other words, respiratory effects are “likely real, but not yet definitive.” Multiple 2025 systematic reviews — including those published in Cureus and Springer’s Internal and Emergency Medicine — reached similar middle-ground conclusions.
Even short-term exposure has been associated in some studies with elevated blood pressure, heart rate, and reduced vascular endothelial function. Cardiovascular concerns cannot be dismissed either.
Conclusion 3: Carcinogenicity, effects on pregnant women, and effects on children are “not yet determinable” (insufficient data)
This is the most important — and most cautionary — finding of the review.
The panel concluded that the following three areas are “currently not determinable”:
- Carcinogenicity from secondhand HTP exposure
- Effects on pregnant women (miscarriage, preterm birth, low birth weight)
- Effects on children (respiratory development, cognitive development, behavioral effects)
The reason is straightforward: long-term follow-up studies are still scarce. HTPs have only been widely available for about a decade. Carcinogenic and developmental effects typically require 20–30 years of tracking to establish.
“Not determinable” is not the same as “safe.” It means “we cannot yet prove this is dangerous, but we also cannot prove it is safe.” This is similar to where combustible cigarettes sat in the 1960s — when the cancer link was “not yet confirmed.”
“Safer than cigarettes” — comparative vs. absolute safety
The HTP debate constantly conflates two distinct questions:
- Question A: Are HTPs less harmful than combustible cigarettes?
- Question B: Are HTPs safe for your health?
Recent international systematic reviews (Cureus 2025, Springer 2025) answer:
- Question A → Yes (likely less harmful than cigarettes)
- Question B → No (risks are not zero. Cardiovascular, respiratory, and metabolic effects are documented)
“Relatively better” and “absolutely safe” are different statements. The MHLW evaluation must also be read with these two questions separated.
For smokers who cannot quit completely, switching from cigarettes to HTPs may function as harm reduction. But starting HTP use because “it’s not bad for you” is not supported by the evidence. This is especially true for non-smokers, young people, and pregnant women, who should avoid them entirely.
International comparison
Public health authorities take notably different stances on HTPs:
| Authority | Position |
|---|---|
| WHO | “Health benefit claims rely heavily on manufacturer-funded research. Independent studies suggest harms” |
| CDC (US) | “Effectiveness as a smoking cessation aid is not established. No tobacco product is completely safe” |
| US FDA | Has authorized certain products as “Modified Risk Tobacco Products” (MRTPs) — but does not allow “safer” claims |
| European Commission | Adopted a 2024 directive banning flavored HTPs |
| Japan (MHLW) | Will reflect this evaluation in year-end regulatory direction |
The global trend converges on roughly the same conclusion: HTPs may be less harmful than cigarettes, but they are not harmless — and regulation is tightening.
Three things you can do now
Translating the evaluation into action for yourself and your family:
1. Don’t use HTPs indoors. Don’t let others use them around you.
The clearest finding is that air becomes contaminated. In spaces shared with family, children, or others, even HTP use should happen outdoors at minimum. Window ventilation, exhaust fans, and balconies with roofs do not prevent indoor spread.
2. If using HTPs as a quit aid, set a deadline.
Harm reduction is a legitimate strategy. But “HTPs forever” carries unknown long-term risks. Combine HTP use with proven cessation tools — clinic-based smoking cessation programs (covered by health insurance in Japan), nicotine replacement therapy (patches, gum) — and aim for zero as the final goal.
3. Don’t start. Young people and pregnant women should avoid them entirely.
Beginning HTP use because “it seems safer than cigarettes” is not supported by the evidence. Adolescents (whose lungs and brains are still developing) and pregnant women (where fetal effects are unknown) should avoid HTPs in all cases.
Summary — the real message of the review
The MHLW 15-year review sides with neither HTP advocates nor opponents. It delivers a sober reality check:
- The air becomes contaminated (strong)
- Respiratory effects on bystanders are suggested (moderate)
- Long-term effects on cancer, pregnancy, and children are not yet known (unknown)
The single most important point: do not read “unknown” as “safe.” The regulatory direction emerging by year-end will be built on this premise.
For HTP users worldwide, this is neither good news nor a warning. It is, simply, an update to the information you need to make your own choice — armed with what the science actually says.
References
- MHLW Council on Health Sciences, Tobacco Health Impact Evaluation Committee (May 21, 2026 materials)
- Science Council of Japan, “Understanding the Toxicity of Heated Tobacco: Toward Evidence-Based Policy” (September 2023)
- Cureus (2025), “Assessing the Health Impacts of Heated Tobacco Products Compared to Traditional Tobacco Use: A Systematic Review”
- Internal and Emergency Medicine, Springer (2025), “Heated tobacco products vs conventional cigarettes: a scoping review of cardiovascular and respiratory clinical outcomes”
- WHO Report on the Global Tobacco Epidemic 2023
- CDC, “Heated Tobacco Products” official page
- European Commission, Tobacco Products Directive 2024 amendment
Evidence level: Level 2 (government-led 15-year systematic review with multi-country replication)
