Atopic eczema (AE) is a skin condition that is often measured by transepidermal water loss (TEWL), a mark of dry skin. The ailment is often associated with the colonization of Staphylococcus aureus and dysfunction of the skin barrier (a few months ago we had a long blog post about atopic eczema and S. aureus so if you're interested in this topic, take a look at that post as well). A group of scientists in Oslo set out to find if whether S. aureus colonization in the nasal cavity or the back of the mouth, the fauces, led to increased TEWL in healthy infants and those with eczema. They also set out to identify if TEWL on the upper arm and forearm provide similar associations between TEWL and atopic excema.
In the study published in PLoS One, 240 infants were enrolled and 167 of them met the requirements. Three study groups were included, those with no eczema, those with possible eczema, and those with eczema. Three samples were taken from the upper arm as well as three samples from the lower forearm.
They found that TEWL measurements from the upper arm and lower forearm were equally appropriate which is important because measurements are generally taken from the lower forearm. Taking measurements is often difficult in these young infants so the ability to take measurements from the upper arm would be seen as an advance as it is more readily accessible.
The scientists also found that while 53% of the infants in the study had S. aureus colonization in the back of the nose and back of the mouth, this was not associated with higher levels of TEWL or atopic eczema. This lack of association differs from previous studies (such as the one I linked earlier) that have shown correlations between S. aureus colonization and atopic eczema. Other human studies have also shown associations with S. aureus on the forehead and cheek and increased TEWL.
The reason for these discrepancies may arise from several different factors including age and sampling site. Adults generally have lower TEWL than infants and this study sampled the bacteria in the nose and mouth while other studies sampled on the eczematous or normal skin directly. While this study does not show a correlation between S. aureus colonization in the mouth and nose with atopic eczema, more work is needed to better understand differences between these studies and what the role of this bacteria is on the condition.