People have been warned against paying for unnecessary, invasive and costly private health screening.
The UK National Screening Committee (NSC) said an increasing number of patients were seeking "reassurance" over their health.
But many are paying for tests that are available on the NHS, the independent body said. The publicly-funded NSC has issued guidance on what stages of life people should be screened for various conditions.
Dr Anne Mackie, director of programmes at the UK NSC, said some people were putting themselves through "unnecessary" anxiety.
"Patients are increasingly turning to private screening companies for reassurance about their health and we hope this guidance will allow them to make the decisions that are best for them. The safety of patients is the most important factor," she said.
Steven Laitner, a GP and consultant in public health medicine, said some tests can pose health risks if undertaken "outside of internationally recognised criteria". Private tests cost from about £125 to £2,000.
The NSC guidance highlighted that men and women aged between 60 and 69 are offered bowel cancer screening every two years. Men are given the option of abdominal aortic aneurysm screening in their 65th year, while breast screening is offered to women between 50 and 70 every three years.
Cervical screening is available to 25- to 49-year-old women every three years and those aged 50 to 64 every five years. Diabetic retinopathy tests are offered to diabetics annually from the age of 12. There are six antenatal and newborn screening programmes.