10 General assessment of possible risks by use of headphones and hearing protection aids

Survey of chemical substances in headphones and hearing protection aids

The survey part of this project has given little information about which materials and possible additives that get into contact with the skin. However, the description of the product group shows that there are significantly more contact areas than just the ear pads and earplugs which initially were judged to be most important. In principle, all securing parts can get into contact with the skin, i.e. that also the materials in various types of spring bands (over head, around the ear, behind the neck) and external components in loudspeakers/loudspeaker houses can get into contact with the skin. For certain broad types of padded spring bands it is probable that the skin contact from the spring band for bald-headed persons is of the same order of magnitude as for the skin contact from the ear pads.

In section 8.3.2 an estimate is given of the amount of few, selected substances which are found in a given product. The estimate is made by multiplying the analyzed amount (in mg/kg) with the estimated weight of the component in which the substance appears. The calculations show that the total amount of potentially problematic substances in the materials getting into contact with the skin is very small. This is in good accordance with the conclusions from Survey project no. 27 and no. 28 of earplugs where calculations are made showing that the tolerable daily intake of selected substances are not exceeded even if the full amount migrates and the product is replaced every day. With the same preconditions, this conclusion will probably be even more noticeable for headphones and hearing protection aids as these products have a lifetime which for quality products is several years.

However, it shall also be noticed that the estimates in section 8.3.2 are only made for a few, selected substances which had the common characteristic that they were only found in very small amounts. For additives like phthalate-based plasticizers there might be significantly larger amounts which in theory can migrate from the product to the body. However, a significant exposure requires that the products are put into the mouth which is not very probable. A realistic, but conservative suggestion of the accessible amount of softeners can be calculated from the following parameters:

Thickness of material: 0.2 mm
Areal in contact with the skin: 30 cm² x 2
Content of softener: 40%
Specific gravity of plasticizer: 1 g/cm³

With these preconditions the maximal accessible amount is 0.48 gram. No migration analyses have been made in this survey but if it is assumed that phthalate content, migration factors (skin penetration 5%) and contact area correspond to those being used in the assessment of the exposure of pencil cases and school bags (Svendsen et al., 2007), there is a high Margin of Safety. In extreme cases, there might be an exposure time which is 8 times longer (8 hours instead of 1), but even for a child of 12 kg the Margin of Safety with these preconditions will be larger than 25,000.

A few producers mention that some users experience skin rash and irritation when using headphones. However, this cannot be regarded as a risk for the health. On the other hand, allergenic reactions to substances which migrate to the surface of headphones and hearing protection aids are probably a larger risk than the risk of systemic effects. The products are in close contact with the skin, often daily and during a long period, and therefore the presence of allergenic substances causes a large potential of eliciting a reaction.

It is also this issue which is of largest concern for both producers and users. The analysis and the assessment of a headset (see section 8.3) focused on the allergenic reactions and even if the conclusion was that the risk was minimal it is underlined in the assessment that there might be other allergenic substances in the product than those being analyzed for. In the larger perspective it must also be considered that it is only a limited selection of materials which has been analyzed.