Human beings have been exposed for millennia to the products of natural combustion that contain semi-volatile organic compounds (SVOCs) such as polycyclic aromatic hydrocarbons (PAHs). Today, however, synthetic, human-made SVOCs are ubiquitous in modern indoor environments and consumer products. They are included as active and very useful ingredients in cleaning agents, pesticides and personal care products such as cosmetics, hair sprays and shampoos, and are substantial additives in vinyl flooring and carpet tiles, furnishings and electronic components. As an additive, SVOCs are used to improve the flexibility and durability of plastic materials, and they are also used as softeners and lubricants or as carriers of other substances in sprays. They act as water reducers in concrete mixtures such as gypsum, making them more workable and easy to mix. Plasticisers used in PVC materials, which are the most common SVOCs, can vaporise from the surface of products as they are not "bound" to the materials. The "new car” smell, for example, is caused mostly by plasticisers evaporating from the car interior in an enclosed environment.
Although people may inhale air containing gaseous SVOCs, or SVOCs adsorbed on airborne particles, exposure to these chemicals may take other forms than inhalation. These SVOCs don’t simply stay up in the air: a large proportion of them become attached to indoor surfaces, without bonding, or to micro-particles of dust. Thus, in the case of young children, exposure may more often take place via touching SVOC-coated surfaces or ingesting contaminated dust. This is a particularly important exposure route among infants. This also explains their persistence indoors over several years, even once the original sources have been removed, in the same way as persistent organic pollutants (POPs) in the outdoor environment. They can also react chemically with indoor ozone (mainly coming from the outdoor air) and other indoor VOCs.
Some SVOCs have been associated with allergic reactions and respiratory symptoms, while others, such as dioxins and pentachlorophenol, are known to be toxic. Some SVOCs, such as polybrominated biphenylsare, are no longer used because of demonstrated or suspected health effects. Environment and health concerns are emerging in relation to other SVOCs that are considered to be endocrine-disrupting chemicals (EDCs): flame retardants, phthalates, pesticides, antimicrobials and polycyclic aromatic hydrocarbons. Exposure to EDCs may occur via multiple routes, but of particular concern is in utero exposure. Endocrine disruptors are thought to interfere with the hormonal systems of humans and wildlife, which can result in a wide range of developmental and reproductive abnormalities. Several institutions worldwide (including the United States Environmental Protection Agency and the European Commission) have adopted strategies to counteract the risks posed by EDCs, and many activities, supported by continuous research, are currently being implemented. In an ongoing process, certain SVOCs that are strongly suspected of posing health risks are being phased out by manufacturers and replaced with new SVOCs, such as bio-plasticisers, which are also biodegradable.
Elevated risks of indoor exposure to high concentrations of SVOCS have been reported in relation to daily cleaning activities, renovation work, the use of materials connected to flooring installation (primers, screed, adhesives, floor coverings), new furniture, wallpaper, carpets and textiles.