Reply to [PERSON]; [PERSON], [PERSON] Comment on \"[PERSON]; [PERSON] ICNIRP Guidelines' Exposure Assessment Method for 5G Millimetre Wave Radiation May Trigger Adverse Effects. _Int. J. Environ. Res. Public Health_**2023**, _20_, 5267\"  
[PERSON], and [PERSON], [PERSON] ICNIRP Guidelines' Exposure Assessment Method for 5G Millimetre Wave Radiation May Trigger Adverse Effects. _Int. J. Environ. Res. Public Health_**2023**, _20_, 7031. [[https://www.mdpi.com/journal/ijerph/2023/14/1](https://www.mdpi.com/journal/ijerph/2023/14/1)]([https://www.mdpi.com/journal/ijerph/2023/14/1](https://www.mdpi.com/journal/ijerph/2023/14/1))  
Our reference to \"homogeneous models\" of dermal tissue was intended to highlight the problem of under-estimation that such models can produce, as revealed by the cited stratified model assessed by [PERSON] et al. [6]. [PERSON] and [PERSON] point out that we have overlooked some multi-layer models cited in the ICNIRP 2020 Guidelines. Two of the three papers they provide as examples include authors [PERSON] and [PERSON], who were part of the ICNIRP Commission at the time the 2020 Guidelines were developed, so we do not regard these as suitably independent models to cite when critiquing ICNIRP's Guidelines. We take this opportunity to add the following italicized words to the first paragraph in question (from the third page of our paper): \"It needs to be borne in mind that _several_ skin modelling studies treat the skin as homogeneous dermal tissue although it is a complex organ interacting with the environment... The induced temperature increase _in such models_ can be underestimated by more than a factor of three\" [7]. The other suggested paper ([PERSON] et al. [8]) includes the authors of the comment under discussion, and it could have been well cited in our paper which is under discussion here. Three of its authors, [PERSON], [PERSON], and [PERSON], have also published a useful review of the thermal response of human skin to microwave energy (30-300 GHz) [9]. In that review, the authors make several interesting points that are pertinent to this discussion:  
* Their literature search found very few studies on heating in human tissue at 5G-relevant frequencies, and those studies' limitations were \"striking\" (p. 539). * Using these data, they developed a thermal model of \"extreme simplicity [with] a number of drastic approximations\" (p. 529) for estimating mmW exposure levels for small areas of skin. * They recommended it as suitable \"to aid in the development and evaluation of RF safety limits at frequencies above 3 GHz and for millimeter waves\" (p. 528), although there were very few data available on small skin-area exposure longer than a few minutes. We note that the paper, and presumably its model, was indeed used in the development of the ICNIRP 2020 Guidelines [10]. * They acknowledge that the Pennes' bioheat equation on which they base it \"does not account for short-range variations in temperature in the immediate vicinity of thermally significant blood vessels\" (p. 536). * There are \"rather few\" thermal models, including theirs, that have been \"validated using data that are independent of those used to develop the models... Consequently their generalizability is uncertain\" (p. 539). * IEEE C95.1-2005 has critiqued some important limitations of various models for testing thermal compliance models, concluding, \"Until these limitations can be resolved, thermal models are useful but in and of themselves are not sufficient for a safety standard development\" (p. 538). * In small, local irradiated areas, \"the temperature increase at the skin surface is chiefly limited by conduction of heat into deeper tissue layers\" [9] (p. 528). Yet, that deeper heating is not assessed by ICNIRP 2020 Guidelines for mmW exposures. We agree that many research questions remain, especially with respect to the best method of assessing near-field exposure from handsets transmitting at millimeter wave frequencies.