Physiological effects of millimeter-waves on skin and skin cells: an overview of the to-date published studies

Introduction

The currently ongoing deployment of the fifth generation of the wireless communication technology (5G) is being met with a great enthusiasm by the telecommunication industry, national governments and portion of the general public. However, there is also some resistance from the part of the population in various locations around the globe.

The opposition towards the deployment of the 5G is caused by the uncertainty whether radiation emitted by the 5G networks and devices will have any effects on human health and environmental impact on fauna and flora.

The 5G wireless communication technology that is being deployed comprises of parts of the used already 3G and 4G technologies. The radiation emitted by the predecessors of the 5G, the radiation frequencies emitted by the 3G and 4G technologies, has been classified by the International Agency for Research on Cancer(IARC), as possible human carcinogen. The IARC evaluation did not concern the frequencies above 6 GHz, especially the currently prepared for use 26 and 28 GHz bands and the whole spectrum of 30–300 GHz frequencies that will be used in coming years. The currently deployed 5G will be supplemented with a new technology that uses the millimeter-waves (mm-waves) for the fast transfer of large amounts of data. Right now, the 5G technology expands into the frequencies below the 6 GHz. Later on, the 5G will use also the frequencies of 6–30 GHz and, still later on, frequencies of mm-waves (30–300 GHz). Currently, in Europe, the spectrum of 26 GHz (range 24.25–27.5 GHz) and 28 GHz (range 26.5–29.5 GHz), is being freed for the 5G use.

It is well established that the 26 and 28 GHz frequencies and mm-waves penetrate only few millimeters inside the human body and are efficiently absorbed by the water content of dermis layer of the skin. This fact has been used to misleadingly portray mm-waves as unlikely affecting the physiology and health of human body because the depth of penetration is only skin deep and does not reach any internal organs.

The question

Do we know enough about the interactions between skin and skin cells with mm-waves to determine what health impact, if any, will have the acute and the long-term (life-time) exposure of skin to mm-waves?

In order to answer the question, literature search was performed to find studies where skin and skin cells were examined following exposure to mm-waves and affected functions and properties of skin and skin cells were evaluated in the context of the possible impact, or lack of it, on human health.

In this brief opinion review is presented evidence on the physiological effects of mm-waves exposures on human volunteers, on laboratory animals and on human and animal cells grown in the laboratory.

The skin

In the research examining the effects of mm-waves, skin is simplified into three major components, the stratum corneum consisting of mostly dead cells, the epidermis consisting of few layers of cells where the bottom layer is made of dividing cells that continuously regenerate the epidermis and the underlying dermis layer. The water content of the skin is what determines the depth of penetration of the mm-waves into human body, limiting it to just couple of millimeters.

From the point of view of water content of the skin, the top layer of the skin, the stratum corneum, has low water content 15–40%, whereas the water content the rest of the skin, epidermis and dermis, is ca. 70–80%. Thus, mm-waves energy penetrates the stratum corneum but is efficiently and effectively absorbed by the water in epidermis and dermis layers [1].

Skin is the largest organ of human body that not only functions as kind of “overcoat” but is involved in regulation of physiological processes that impact the functioning of the whole body.

Skin has different thickness, color, and texture in different locations over the body and performs number of important functions. Skin (i) regulates immune response by both mechanically preventing entry of microorganisms and biochemically by generation of molecular mediators that are distributed with blood circulation to internal organs (ii) regulates body temperature, (ii) stores water and fat and prevents water loss, (iii) functions as sensory organ, and (vii) helps to make vitamin D when exposed to the sunlight.

Skin is composed of a variety of cell types that perform various functions. In epidermis reside keratinocytes, melanocytes, Merkel cells, and Langerhans cells. The dermis consists of connective tissue cells and extracellular matrix and there are located numerous nerve endings that provide the sense of touch and heat, the hair follicles, sweat glands, sebaceous glands, apocrine glands, lymphatic vessels and blood vessels. Furthermore, the skin surface provides an environment for over thousand identified species of microbes.

Different pathological conditions affecting skin might have impact on how the skin and skin cells perform their functions and how they might react/respond to mm-waves exposure. These skin ailments, that will affect levels of water in the skin, include dermatitis, eczema, psoriasis, dandruff, acne, cellulitis, skin abscess (boil or furuncle), rosacea, warts, melanoma, basal cell carcinoma, seborrheic keratosis, actinic keratosis, squamous cell carcinoma, herpes blisters, hives, tinea versicolor, viral exantham, shingles, herpes zoster, scabies, or ringworm [2].

Therefore, skin is not just a thin overcoat on the surface of the human body but it is an aggregate of numerous cells and microorganisms living together and playing a crucial role in regulating of the health and wellbeing of human body. As Sanford and Gallo [3] pointed out in their review article:

“…The skin, the human body’s largest organ, is home to a diverse and complex variety of innate and adaptive immune functions […] the skin immune system should be considered a collective mixture of elements from the host and microbes acting in a mutualistic relationship…”

Discussion

The current use of the 3G and 4G technologies and the ongoing deployment of the 5G technology, where the number of base stations will increase dramatically, has reignited the health debate around the radiation emitted by these wireless communication technologies.

The new aspect of the 5G technology that will differ dramatically from the earlier technologies will be the use of mm-waves, where both, antennas and devices will be in very close proximity of the users, affecting the exposure patterns. In some countries, deployment of the 5G technology, using mm-waves for public use, has already begun what adds to the health-related stress of uncertainty in some part of the to-be exposed population.

When evaluating the health risk of any agent, the scientific evidence taken into consideration by the health regulatory authorities consists, in order of importance, of the following types of research studies:

  • Epidemiology studies
  • Human volunteer studies
  • Animal in vivo studies
  • Laboratory in vitro studies

The epidemiology studies are possible to execute only after the technology has been deployed and sizable parts of the population are being exposed to the examined agent, in this case the mm-waves radiation emitted by the 5G technology. Thus, this considered to be the most important and relevant scientific evidence is currently not available and will not be available for several years.However, the remaining three types of studies are possible to execute, and should be executed, before the deployment of the 5G technology, in order to determine whether any risk of health effects exists.

Skin is the only organ of the human body, besides the eyes, that will be directly exposed to the mm-waves of the 5G technology. As presented in this review, the whole scientific evidence on the possible effects of mm-waves on skin and skin cells consists of only some 99 studies, where 11 are human volunteer studies, 54 are animal in vivo studies (rats & mice) and 34 are in vitro laboratory studies using human and animal cell cultures.

These studies examined only short-term acute effects of the exposure that do not provide any information about the possible delayed or long-term-exposure effects. Furthermore, the effects of mm-waves were examined in separation from other frequencies used by the wireless communication technologies and in separation from other environmental stressors. Possibility of any co-effects and/or synergistic effects, between mm-waves and other environmental stressors, were not examined at all.

This clearly indicates that the scientific evidence concerning the mm-waves effects on skin is extremely very limited. The evidence from the 99 studies is insufficient to make any reliable, science based evaluation of whether the mm-waves will have or will not have any health effects.

Besides the sheer number of executed studies, of importance in the analysis of the available scientific data are the types and number of performed studies, the size of the studies, the following of the good laboratory practices used when performing studies, whether the results obtained in one laboratory were possible to replicate by other research groups, and, finally, the number of the research groups that were involved in generation of the data. Scientific data from a single research group, no matter how extensive and well executed, need corroboration from other researchers. The research on mm-waves has been dominated by the research teams in Reims, France and in Philadelphia, USA, and their findings require replication studies from other research groups.

The very limited evidence, stemming from the 99 presented studies, suggests that some biological and physiologically relevant effects might be induced in skin and skin cells by exposures to mm-waves. However, this evidence is currently insufficient to claim that any effects have been proven or disproven.

Therefore, the usefulness of the to-date executed research on mm-waves effects on skin is of a very limited use because for developing protective measures for the users because:

  • Firstly, as mentioned above, only a small number of studies examined mm-effects on skin and skin cells.
  • Secondly, there is only a very few human volunteer studies.
  • Thirdly, the majority of research are small experimental studies performed on animals (rats, mice) or cells grown in laboratory. While such studies are important, they are predominantly used to corroborate the evidence obtained in epidemiological and human volunteer studies. Results of animal and in vitrostudies alone are not sufficient to formulate basis for human health policy and for human exposure limits.

Therefore, the recently published guidelines by the International Commission on Non-Ionizing Radiation Protection (ICNIRP) [103], stating that the ICNIRP proposed mm-waves radiation exposure limits are protecting users form health effects of mm-waves are only an assumption that is not sufficiently based on scientific evidence because the research on effects of mm-waves on skin has not been performed. This is why any claims, including ICNIRP’s, that the current safety limits protect all users, no matter of their age or their health status, have no sufficient scientific basis. The safety limits that are suggested to protect from health effects of mm-waves are based on scientifically unsupported assumptions as seen from the evidence presented in Tables 1– 4.Another serious problem of how the 5G mm-waves employing technology is being presented to the future users is the misrepresentation of the role the skin plays in regulation of the whole body’s physiology. The notion, often presented in the news media, that mm-waves will not be of health concern because mm-waves are entirely absorbed by epidermis and dermis layers, is misleading. Indeed, mm-waves are absorbed in the skin and do not penetrate deep enough to reach any internal organs. However, the skin is not just a “physiologically inert overcoat” shielding body from the environment. Skin is involved in regulation of the immune response as well as other body functions (cardiovascular functions, neurological functions) through release of a variety of molecular mediators generated by the skin cells in response to environmental stressors, like e.g. mm-waves.

Considering the very limited research on the effects of mm-waves on skin, there is an urgent need for research on effects of mm-waves on humans. Some of the studies is possible to execute, in ethical manner, using human volunteers. Toxicology studies, on mice and rats, using standardized protocols, like those used by the National Toxicology Program in USA, are urgently needed. In vitro laboratory studies should, preferably, use primary human cells or human cell lines. Studies using high-throughput screening techniques of transcriptomics, proteomics and metabolomics should be used to analyze the ethically available tissue samples obtained from human volunteers to determine the molecular level responses of human body to the mm-waves. Data obtained from the molecular high-throughput screenings can then be used to formulate research hypotheses for testing. Epidemiological studies might not be possible to execute as long as the 5G networks are not deployed and people are not exposed as a population.

Because of the lack of sufficiently robust scientific data on mm-waves effects on human skin, precautionary measures should be recommended, whenever possible and feasible when dealing with the mm-waves exposures. These precautionary measures can be e.g. postponing or limiting the 5G deployment in residential areas. It should be considered that not everything and not everywhere needs to be 5G wirelessly connected. Use of fiber optics connections, that will be used to connect 5G base stations, should be used as extensively as possible to limit the deployment of radiation-emitting devices, especially those in close proximity to people and within people dwellings. Deployment for industrial use should be the first but the further, broader deployment for the non-industrial use, should preferably await for the results of the bio-medical research.

Conclusion

In conclusion, there is an urgent need for research on the biological and health effects of mm-waves because, using the currently available evidence on skin effects, the claims that “we know skin and human health will not be affected” as well as the claims that “we know skin and human health will be affected” are premature assumptions that lack sufficient scientific basis.

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