Dating apps are partly to blame for a rise in sexually-transmitted infections, experts believe.
The hot weather may also have helped cause a steep increase in syphilis because people are more sexually active when it is sunny.
One health board has seen five times as many cases in the past four months compared with the same period in 2017.
Most have been men but several women also tested positive.
Doctors suspect it’s down to more people using dating apps such as Tinder and Bumble to meet for unprotected sex.
Users often delete partners’ profiles afterward, preventing them from warning if they are later diagnosed with an infection.
Health experts are urging people to contact a sexual health clinic if they have had unprotected sex in recent months.
Lead nurse Joanne Hearne said: “There has been an increase in syphilis.”
“It is possible that the heatwave led to people becoming more sexually active.”
“We also believe social media and the growth of dating websites and apps is another contributory factor.”