Testing for cervical cancer among women in England has fallen to a 10-year low, a cancer charity said.
Despite cervical screening saving 5,000 lives every year in the UK, 20% of women are not being tested.
The charity said many feel the screening is not necessary or relevant to them, while others are unaware of the causes, symptoms and ways to prevent the cancer.
Some women miss or delay tests because of work commitments, while others book time off work because they are too embarrassed to discuss it with their bosses.
Jo's Cervical Cancer Trust - the UK's only dedicated cervical cancer charity - is urging more women to attend screenings.
– Jo's Cervical Cancer Trust director Robert Music
The screening programme saves 5,000 lives each year in the UK yet 20% of women are not attending their cervical screening test. The more we can do to stress the importance of this life-saving test the better.
"With such a worrying decline in numbers our campaign is also targeting key cities where uptake is below the national average."
The "Jade Goody effect" saw more than 400,000 women in England tested for cervical cancer between mid-2008 and mid-2009.
It said a poll, carried out by YouGov, showed that since then numbers have declined.
Now fewer than 80% of women take up the screening - more than one in five women between the ages of 25 and 64 and one in three under 35 are not being tested.
Women over 50 being screened dropped below 80% for the first time in 2010 and fell even further last year.
Jo's Cervical Cancer Trust said some women found the screening unnecessary or not relevant to them.
Others struggled to understand the information they received and more showed a lack of awareness about the causes, symptoms and ways to prevent cervical cancer.
Work also got in the way of screenings, and a survey found that if doctors were more flexible about appointment times it would encourage women to make screenings more of a priority.
– Health Minister Simon Burns
In 2009, we saw Jade Goody tragically lose her brave battle against cervical cancer.
"That led to a large increase in women coming forward for screening. The screening figures from 2009 confirm what an impact Jade's fight had on women across the country.
"We urge women when they receive this invitation to consider going for screening as we know this can save lives."