Skin is the body’s first line of defense against the external environment and exposure to recreational water can compromise the skin’s protective functions. Recreational water often contains harmful algal blooms and cyanotoxins, pathogenic bacteria, antibiotics and antibiotic resistance genes. This research investigated the following effects of recreational water exposure on human skin: cyanotoxin skin penetration potential, changes in the human skin microbiome and acquisition of exogenous antibiotic resistance genes (ARGs), antibiotic biosynthesis genes (ABSGs) and virulence factor genes (VFGs).

Cyanotoxin penetration potential was investigated in an in-depth examination of the state of knowledge on cyanotoxins and their potential to cause negative health effects through dermal permeation. Epidemiological and toxicological studies of the health effects from algal toxin exposure are summarized to highlight the importance of better understanding of the effects on human skin. This research identified a disparity between the human health effects described in epidemiology case studies and toxicological dermal exposure data indicating potential dermal penetration. The penetrative abilities of specific cyanotoxins were predicted by their physiochemical properties indicating the potential for skin penetration. These predictions and the known comprehensive algal toxin data can be used to better evaluate human health risks.

Another component of the skin’s protective role is the microbiome, which has been shown to provide immunity against exogenous bacterial colonization. This study explored the link between ocean water exposure and the human skin microbiome demonstrating that there are post-exposure alterations. Skin microbiome samples were collected from human participants’ calves before and after they swam in the ocean, and at 6 hours and 24 hours post-swim and were analyzed using 16s rRNA gene and metagenomic sequencing. Beta diversity analysis revealed that the skin microbial communities on all participants before swimming were different from one another, but immediately after swimming, all participants’ microbial communities were tightly clustered, indicating that the communities were no longer different. Taxonomic analysis showed that ocean bacteria, including potential pathogens, replaced the native skin bacteria and remained on the skin for at least 24 hours post-swim. Metagenomic analysis and functional gene predictions showed that ARGs, ABSGs and VFGs present on the skin increased in diversity and abundance after participants swam in the ocean and persisted for at least 6 hours post-swim. This research provides insight into the relationship between human health, the skin microbiome and the environment.