Sixteen studies were included (n=772): three RCTs (n=254); a randomised crossover trial (n=54); one experimental paired/crossover study (n=6); six case series (n=259 cases); and five review articles (n=199).
Two RCTs and one randomised paired comparison looked at nematocyst-type stings. In one study heat reduced pain scores at five and 10 minutes after application (odds ratio 5.2, 95% CI: 1.3, 22.8, p<0.05) compared with placebo. A second study reported lower pain scores with hot water immersion at four (p<0.001) and 20 minutes (p<0.001). In the final study the trial was stopped because hot water immersion was shown to be more effective (p=0.002) after 20 minutes.
Data from a randomised crossover trial (n=27 in each arm) compared hot showers and ice packs reported that hot showers reduced total treatment time and pain, with complete cessation of pain for 48 per cent (p<0.01) of those treated with hot showers. All of these studies were methodologically flawed.
One experimental paired/crossover study comprised six volunteers in which pain was relieved after 30 minutes of hot water immersion. Six case series studies comprised 259 cases of marine envenomation with 135 cases treated with hot water, from which 122 reported a reduction in pain.