You might not be familiar with “thread veins," but a good number of women have them. And apparently a lot of these women are getting them removed for the sake of having a smooth-looking tummy to expose in crop tops, including celebrities.

There has been a 20 percent increase in the numbers of young women, mostly aged 20 to 40 years old, who are getting thread veins removed, according to experts at Dr. Newmans Clinic — a network of thread vein removal clinics in the UK. “Whereas the top two most common areas women have thread veins treated are on their faces and legs, recently we have seen a sharp rise in the number of 20 to 40-year-old women coming in with concerns about thread veins in the subcostal margin, and this area is now the third most common part of the body for treatment,” Dr. Peter Finigan, medical director at Dr. Newmans Clinic, told the Daily Mail.

Some women may have a genetic predisposition for thread veins on their stomach, but others develop thread veins from heavy drinking, copious amounts of sun, hormones, and pregnancy. They are essentially small blood vessels that show through the surface of the skin and appear to be fine red or purple lines — they’re also sometimes referred to as spider veins.

“Many patients tell us they feel self-conscious wearing a bikini or crop top if they have thread veins in this area — which usually appear in a ‘belt’ of tiny, vertical red lines,” Finigan said. “Interestingly, the patients we have treated for this area over the last 12 months have been getting younger, with the majority aged between 20 and 30 years old.”

Removing thread veins can be accomplished through several different procedures — such as lasertherapy, sclerotherapy, or a mix of both. In lasertherapy, doctors use laser light to destroy small blood vessels. But veins that are bigger than 4mm need to be removed with sclerotherapy, which involves using a tiny needle to inject a solution that damages cells lining the vein, causing the vein to shrink and disappear over eight weeks. But there’s also a chance that sclerotherapy could cause some complications, like bruising or itching, or a discoloration of the skin. About 10 percent of people experience “matting” after sclerotherapy, meaning small vessels develop in clusters, but this usually clears up after a while.

Is it possible that older women are less likely to undergo thread vein removal because they're simply less concerned with exposing their midriffs and looking sexy in selfies? “We do also treat older women up to the age of 40,” Finigan said, “but patient numbers tend to fall after this age. This could be down to older women preferring not to bare their midriff, or perhaps becoming more body confident as they get older.”