I just read the article. Very interesting, indeed.
The article contains a section about potential inflammatory agents in semen (which cause skin reactions in both patients and controls):
Human seminal plasma has a variety of inflammatory cytokines and chemokines including TGF-β1, CXCL8 (ex-IL-8), GRO (CXCL1/Th17), monocyte chemotactic protein 1 (MCP-1), IL-13, nd IL-17 [11], some of which can activate basophils or mast cells; for example, Conti et al. [12] showed that MCP-1 has chemotactic activity for mast cells and plays a fundamental role in the release of histamine. Geiser et al. [13] reported that IL-8 and GRO proteins were active toward basophils as indicated by chemotaxis and intracellular calcium changes in concentration. In addition to the presence of these immunologic factors in seminal plasma, high concentrations of spermine (2?15 mmol/L) were observed in seminal fluid
[14]. This may injure endothelial cells. Yang et al. demonstrated that 200 μmol/L exogenous spermine can induce injury to human umbilical vein endotheliocytes. It is here supposed that these substances may directly stimulate the skin and cause wheals and erythema when injected into the skin of both patients and healthy controls.
The article also suggests another hypothesis. I quote:
The symptoms of POIS are similar to those of ?opioid withdrawal syndrome,? which includes physical (flu-like symptoms, perspiration, and rhinitis) and psychological symptoms (anxiety, depression, and difficulty concentrating). These symptoms can last 2?7 days [15]. Opioids are involved in mediation of positive affective states generated by the execution of sexual behavior [16]. The μ-opioid receptors are thought to play a crucial role in controlling this behavior [17]. We supposed that patients suffering from POIS may have a disorder of the endogenous μ-opioid receptor system. Orgasm consumes large amounts of endogenous opioids in these patients, which causes a series of symptoms similar to opioid withdrawal symptoms. In addition, the patient was diagnosed with insomnia, anxiety, and slight obsessive?compulsive disorder; these psychological factors may increase awareness to body?s changes.
I also came across another article which discusses the usefulness of skin-prick tests for detecting immunology against semen:
Tal, Yuval, Jonathan A. Bernstein, Miriam Lorberbaum, Debajyoti Ghosh, and Zvi Dranitzki. ?Is Skin Testing Reliable for Confirming Sensitization to Seminal Fluid Proteins?? The Journal of Allergy and Clinical Immunology: In Practice 2, no. 6 (November 2014): 798?99. doi:10.1016/j.jaip.2014.08.006.
Unfortunately, I cannot access that article. If someone can, I'd be happy to have a look at it.
http://linkinghub.elsevier.com/retrieve/pii/S2213219814003870