Response to Shihadeh et al. (2015): E‐cigarettes generate high levels of aldehydes only in ‘dry puff’ conditions

We were particularly surprised by the content and the verbal style of the 'Letter to the editor' by Shihadeh et al. 1. The authors question the peer-review process of the journal and the validity of our findings on aldehydes release in normal vaping conditions and during dry puffs 2. However, their strong and aggressive wording is poorly substantiated. Although we will explain later why the requests for further information from Shihadeh et al. are irrelevant to the purpose of reproducing our study, we take the opportunity to present some more details about our methodology. The participants were supervised by members of the research team when taking puffs with the equipment that was provided to them. A hand-held digital chronometer was used to verify the puff duration and interpuff interval. Obviously, the same conditions were replicated in the smoking machine, meaning that 4-sec puffs and 30-sec interpuff intervals were used. The puff volume was set at 70 ml. As for the information on how many puffs were needed before identifying dry puffs, the vapers identified dry puff conditions on the first puff when used at 9 and 10 W with the single-wick atomizer. The statement 'interindividual differences in detecting dry puffs' refers to the different power levels at which vapers might identify dry puffs. In the Limitations section we more than adequately addressed the fact that more studies are needed, with more atomizers, different liquids and more vapers examined in order to fully identify interindividual differences in dry puff detection. Shihadeh et al. claim that there is a lack of information in the paper that would make replication of the results impossible. It is important to determine what exactly they mean by the term 'reproduce', because it seems that they have missed an important point in our study. The purpose of our study was stated clearly as '…to examine the amount of aldehyde emissions at different power levels associated with both normal and dry puff conditions'. By definition, reproducibility of our study includes identification of dry puff conditions, i.e. asking vapers to identify the dry puffs. Moreover, in our study we used a rebuildable atomizer, which means that the coil-wick setup can only be prepared manually. We prepared the atomizer intentionally with one more and one less efficient setup. Due to the difficulty in reproducing the same atomizer setup accurately, we prepared the atomizers once only and we used them both during the vapers' testing and at the smoke machine. A different setup (even prepared by the same person) could potentially result in different performance characteristics and would require repetition of the tests performed by the vapers. Therefore, reproducing our study is meaningful only by first asking vapers to detect the dry puff phenomenon with the atomizer of choice and subsequently using the same equipment at the same conditions in the laboratory. Although we could discuss extensively about coil and wicking composition, thickness, length and positioning, airflow setup and liquid viscosity, we deliberately omitted this information because it would be irrelevant and it would mislead scientists into thinking that they can reproduce the same conditions at the same power levels without engaging any vapers to test the equipment and verify the generation of dry puffs. The end result could be a repetition of false and misleading claims that have been published and presented previously 3. We repeat that our study purpose was not to test the efficiency of a specific atomizer, but to assess normal vaping and dry puff conditions. What Shihadeh et al. consider 'broad unsubstantiated claims' in the Discussion section are well-known facts that vapers report regularly. Not only is this information derived from experienced users, it is also compatible with common sense. For example, it is expected that low levels of liquid will result in overheating and generation of dry puff conditions; there is no need to conduct a separate study to prove this. The authors' characterization of the dry puff phenomenon as a term with 'tenuous ontological status' further confirms our opinion that the electronic cigarette is an extremely complicated and diverse product, and our observation that it is not unusual for researchers to exhibit a significant lack of understanding about their mode of function and patterns of use by consumers. Thus, we once again recommend researchers to look for appropriate guidance and information from experienced vapers. It is one of the rare cases where we have seen consumers understanding some aspects related to a product (electronic cigartte) use more clearly than researchers. Unless researchers accept that the dry puff phenomenon is a reality and can be properly identified only by vapers, we will not avoid the frustration of seeing headlines grossly misinforming about extremely high aldehyde emissions and carcinogenic potential resulting from unrealistic experimental conditions. The potential of misusing and abusing (whether intentionally or not) electronic cigarettes in laboratory experiments cannot be used as an excuse to present findings irrelevant to true human exposure and create confusion among consumers, scientists and regulators. Finally, it is a paradox that the authors of the letter are accusing us for presenting unjustified conclusions. Shihadeh and Talih co-authored a study characterizing 'direct dripping' as a 'high temperature, high formaldehyde emission electronic cigarette use method' in the title 4. Similarly to our study, they used a single atomizer (in fact, that was an atomizer which might have been popular 3–4 years ago but is now rarely used) and a single liquid. Unlike our study, they used an extreme puffing regimen (8-sec puff duration, 10-sec interpuff interval), which is not representative of average realistic use patterns 5. More importantly, they failed to assess whether the conditions used in the laboratory result in generation of dry puffs. Thus, they verified our concerns and repeated the same mistakes as elsewhere 3. We hope that our study and the detailed explanations and clarifications provided in this response will result in avoiding such mistakes in the future. Some of the studies by K.F. and V.V. were performed using unrestricted funds provided to the institution (Onassis Cardiac Surgery Center) by electronic cigarette companies.