2024-01-31 15:57:37
Although we spend the majority of our time indoors, this does not protect us from air pollution. In fact, many pollutants are found in indoor air, such as chemicals which are used in the composition of building materials, cleaning products, and other furniture or utensils.
These substances can exist in gaseous form (they are called volatile organic compounds), which means we can inhale them. But there are also semi-volatile organic compounds: as their name suggests, these compounds not only exist in gaseous form, but they can also be deposited and persist on surfaces (adsorb there). This includes not only the surfaces present inside the home, but also the dust found there.
However, if these chemicals are able to enter our body by inhalation, by ingestion or by contact with a surface on which they are adsorbed, they can also contaminate us by passing through our skin directly from the ambient air.
Once in our bodies, these substances can harm our health, potentially affecting the respiratory system, nervous system, cognitive health and hormonal system.
Skin exposure
Of the many groups of semi-volatile organic compounds that exist, the phthalate group is the one you are most likely to have encountered. These substances are in fact omnipresent in our environment, and we are almost continually exposed to them.
Phthalates are added to many products to make them softer and more flexible (they are plasticizers). They are found not only in certain types of plastics (like food packaging or garden hoses), but also in different building materials (like vinyl flooring), as well as in hygiene and care products (including shampoos and hair sprays).
Scientific work has established that there are associations between exposure to these chemicals and various health problems, including poorer sperm quality, poorer cardiovascular health, and alterations in growth and development in children.
Once phthalates enter the body, they break down within a few hours to a few days. The decomposition products (metabolites) thus produced are then excreted through urine. But despite this rapid excretion, we almost systematically find traces of phthalates in our bodies. Indeed, we are continually exposed to this family of chemicals during our daily lives, and in different ways.
A misconception that is still too widespread is that we only run a risk of exposure to chemicals if we ingest or inhale them. But various research studies have established that skin absorption has a major impact on the levels of phthalates found in our bodies.
Thus, during a study carried out in 2015, six participants were exposed, in a special chamber, to air containing two kinds of phthalates, at high levels. Concretely, a latex paint containing high concentrations of these compounds was applied to aluminum plates suspended in the room where the participants were.
So that scientists could discriminate the amount of phthalates absorbed through inhalation versus that passing through the skin, the people involved in this study were exposed twice – once while wearing a tight-fitting air-filtering hood (so they were exposed only via their skin) and another time without the hood (they therefore found themselves exposed both through the skin and by inhalation). To increase the surface area of skin exposed, participants were simply dressed in shorts.
Participants were exposed to phthalates emitted by latex paint. Olya Maximenko/Shutterstock
Their diet was controlled, and their use of hygiene and care products was restricted, because as mentioned above, these can constitute a major source of phthalate contamination. After this exposure, they were asked to collect their urine for several days.
It was by measuring the concentration of phthalate metabolites present in these urine samples that scientists were able to estimate the quantity of phthalates absorbed following exposure to paint.
Result: even when only their skin was exposed, the participants absorbed substantial doses of phthalates. Logically, their exposure was found to be higher when both routes of exposure, skin and respiratory tract, were involved.
Clothing can be protective or contaminating
In the same study, an individual participated in a different kind of experiment, to better understand how the skin absorbs these chemicals, as well as to determine whether clothing has a protective effect.
This participant was also exposed to phthalates twice, but while systematically wearing a filtering hood, to ensure that his skin was the only possible route of absorption. During the first experiment, this person wore clean clothes. During the second experiment, the clothes worn were exposed to the air in the room for several days before the participant put them on. The results were then compared to those of participants with bare skin.
The researchers discovered that the participant’s exposure to phthalates was reduced when he wore clean clothes, but that it was three to six times higher when he wore the contaminated clothes (compared to the people who participated in the “bare skin” test). This result reveals that clothing can also constitute a “reservoir” of pollutants.
In 2016, similar results were published. They were obtained in a follow-up study using almost identical experiments, except that the test chemical was nicotine in cigarette smoke. More recently (results published in 2023), research work carried out in the homes of several people (and not in the laboratory) also gave similar results.
Modeling studies have also indicated that perfluoroalkyl and polyfluoroalkyl substances (PFAS), another type of commonly used semi-volatile organic compound, can also be absorbed through the skin.
All these results highlight the potentially significant role of skin absorption in exposure to air pollution – and the protective role of clothing.
What health risks ?
The harm a given chemical can cause differs depending on how it enters the body. Ingested chemicals pass through the intestines and liver before entering the bloodstream. Inhaled chemicals first pass through the lungs, where they can enter directly into the bloodstream. Finally, chemicals that penetrate the skin can also pass directly into the bloodstream. The skin doesn’t even have to be injured, as some chemicals can be absorbed directly through healthy skin.
Furthermore, for similar levels of exposure, the concentration of pollutants within our body differs depending on the route of exposure. For example, one study modeled the concentration in the liver and kidney of a chemical called bisphenol A, depending on whether absorption occurred by ingestion or via the skin. The results revealed that, depending on the route of exposure, the concentrations differed significantly in these two organs.
In conclusion, the more we are exposed to chemical compounds, the greater the likelihood that they will adsorb onto our skin and that it will become a significant route of exposure. Fortunately, it is possible to reduce this vulnerability in several ways:
Use low-emission construction materials (paints, adhesives, etc.) when possible.
Clean interior surfaces to remove any chemicals that may have deposited on them (especially dusty surfaces).
Wash clothes and bedding regularly, as well as new clothes before wearing them. This will help prevent chemical absorption through the skin.
Ventilate your home regularly (unless the home has controlled mechanical ventilation – effective VMC). This will help reduce the concentration of pollutants in the air.
Bathing and washing hands after exposure may also help reduce skin absorption.
By improving indoor air quality, it is possible to reduce the risk of being exposed to multiple pollutants harmful to health.
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