Young people in Cumbria are to be offered free, do-it-yourself chlamydia test kits as part of a campaign.
Staff at 80 pharmacies will offer the tests to the under 25s who ask for free emergency contraceptives.
If undiagnosed and untreated the sexually transmitted disease can leave victims infertile. But if caught early it is easy to treat with antibiotics.
The test involves sending off a urine sample for men and a self-taken swab for women for laboratory analysis.
Andrea Loudon, head of medicines management at NHS Cumbria, said: "It is often women who seek the 'morning after pill' who do so because they've had unprotected sex and also put themselves at risk of infections.
"The kit is easy to use and goes some way towards cutting out the embarrassment some people could feel which could put them off being tested and lead to long term health problems if undiagnosed."
Research shows a large number of cases go undiagnosed because around 50% of infected men and 70% of infected women do not have any symptoms.
Participants with negative results will be contacted via text message, letter or by phone within weeks.
If the result is positive, a health advisor will contact patients personally to discuss treatment.