A record 3.3 million visits were made to sexual health clinics in England last year, as local councils warn over funding cuts and stretched resources.
Figures show there were 3,323,275 visits across the country in 2017, an increase of 13% from 2013.
The extra demand comes at the same time as £600m has been cut from public health spending.
The Local Government Association (LGA) is urging the government to reverse the budget cuts.
The LGA, which represents 370 councils in England and Wales, welcomed the increase in people taking their sexual health seriously but said it would be "hugely challenging" to maintain services at current levels.
It also warned that some areas may struggle to respond to unforeseen sexually transmitted infection (STI) outbreaks unless cuts were halted.
The total number of sexual health screens – tests for chlamydia, gonorrhoea, syphilis and HIV – has risen by nearly one-fifth (18%) from 1,513,288 in 2013 to 1,778,306 in 2017, figures from Public Health England revealed.
A BBC investigation in June revealed that almost half the councils in England were planning to cut spending on sexual health, putting some sexual health clinics at risk of closure or reduced hours as a result.
Of the 151 councils that responded to a BBC Freedom of Information request, 72 planned to cut sexual health funding in 2018-19 compared with 2017-18.
Most said any savings would be made through efficiencies, but 16 councils said services would be cut or reduced.
Councillor Ian Hudspeth, chairman of the LGA's Community Wellbeing Board, said some councils' sexual health services are being pushed to unsustainable levels.
He said: "While it's great to see a huge increase in people taking their sexual health seriously, this rising demand is pushing some councils' sexual health services to peak capacity levels which are not sustainable in the long term.
"Cuts to public health funding need to be reversed as this could affect councils' ability to meet further increases in demand and respond to unforeseen outbreaks of sexually transmitted infections."
Dr Olwen Williams, president of the British Association for Sexual Health and HIV said: "Cuts to sexual health funding have come at the worst possible time.
"Record demand for services, dramatic increases in syphilis and gonorrhoea diagnoses and the spread of treatment-resistant infection in recent years mean that many services are struggling to cope, despite valiant efforts from staff."
He said further cuts would "almost certainly tip them over the edge" and urged the government to reverse its "damaging approach to sexual health".
A Department of Health and Social Care spokesman said: "We have a strong track record on sexual health with teenage pregnancies at an all-time low and sexually-transmitted infections continuing to fall.
"Sexual health services and tests are now more widely available online which means people can get tested at a time that suits them – over 11,000 diagnoses from online tests were reported last year."
The spokesman said the government was giving £16bn to local authorities for public health services over the current spending period.