The study shows that a skin protein called psoriasin shoots up a lot in eczema (atopic dermatitis) and when the skin barrier is damaged, but it doesn’t change the levels of the peptide LL‑37 that many biohackers track. This rise seems to help keep E. coli away, even though other antimicrobial proteins are lower in eczema skin.

The innate defense of the skin against microbial threats is influenced by antimicrobial proteins (AMP). Staphylococcus aureus often colonizes the skin of patients with atopic dermatitis (AD). This was explained by diminished expression of AMP including cathelicidin/LL-37, human beta-defensins-2 and -3, and dermcidin. The S100-protein psoriasin is an additional keratinocyte-derived AMP that preferentially kills E. coli. As E. coli infections are not observed in atopic skin we investigated the functional role of psoriasin in AD patients. Immunohistochemistry demonstrated enhanced epidermal psoriasin expression in AD. An up to 1500-fold increase in secreted psoriasin was detected by ELISA in vivo on the surface of AD skin compared to healthy control skin. Surprisingly, tumor necrosis factor-alpha-enhanced psoriasin release in primary keratinocytes was inhibited by the Th2-cytokines IL-4 and -13, whereas IL-17 and -22 induced psoriasin. Epidermal barrier disruption significantly enhanced psoriasin expression as demonstrated by tape stripping in healthy volunteers. The upregulation of psoriasin in AD maybe induced by the disrupted skin barrier offering a possible explanation why these patients do not suffer from skin infections with E. coli. This indicates that the antimicrobial response in AD is not generally impaired, but greatly differs according to the type of AMP produced by the skin.