What do the barbs (cogs) on thread lift threads do?

Cogs are tiny barbs on the surface of a thread. They catch on tissue under the skin to keep the thread from slipping, and spread the pulling force along the whole thread so lifted tissue stays where it was placed. Smooth threads without barbs have a weaker grip, so barbed threads are mainly used to lift sagging facial contours.

What Cogs Do

Barbed threads do three main jobs.

• Grip: the barbs catch on tissue so the thread stays in place
• Lift: when the thread is pulled upward, the tissue caught on the barbs comes with it
• Spread the load: the pulling force is distributed along the length of the thread instead of concentrating at one point

U.S. FDA records for a barbed PDO thread also state that the barbs hold the thread in place and provide lifting force along the entire thread.

(Evidence: U.S. FDA 510(k) summary, 2023)

How Barb Direction Makes a Difference

Which way the barbs face changes how the thread is used.

• Unidirectional barbs: all the barbs face one way. Used when the end of the thread is anchored higher up to pull tissue upward
• Bidirectional barbs: from the middle of the thread, the barbs on each half face opposite directions, so the thread grips tissue from both sides and holds
• Multidirectional barbs: the barbs run around the thread, gripping tissue in several directions

Even among barbed threads, length, thickness, and barb size and spacing vary by product.

Threads That Use Cones Instead of Barbs

Some threads use small cones threaded onto them instead of barbs. Silhouette Soft is a well-known example.

• Material: a dissolvable PLLA-based material
• How it works: the cones grip tissue through 360 degrees to provide lifting force
• Insertion: each end of the thread has a needle attached, and the thread is placed with the needle

(Evidence: literature review by Korean researchers, 2024)

There are also smooth threads without barbs (mono threads). They're mainly used for skin texture and fine lines and do little to lift sagging tissue.

What Cogs Can Cause

Because cogs grip tissue, that grip can also cause some reactions.

• Dimpling: the spot where a barb catches can look indented
• Tightness: you may feel a catch when you smile or open your mouth
• Asymmetry: there may be a period when the two sides settle differently

An analysis pooling 26 studies on facial thread lifts reported dimpling in about 10% of cases.

(Evidence: meta-analysis by Chinese and U.S. researchers, 26 studies, 2021)

Another analysis pooling 19 studies on dissolvable threads found that barbed threads had more side-effect reports than smooth or cone threads.

(Evidence: review of 19 studies with 1,406 patients, 2025)

In a study of 2,000 PDO thread lifts, skin retraction was the most common reaction, at 6.35%. The risk of side effects also tended to rise with more threads placed and with older age.

(Evidence: study of 2,000 cases across 105 clinics, 2026)

Dimpling usually resolves as swelling goes down, but if it lasts, have it checked at the clinic. Don't rub it hard yourself.

Choosing a Barbed Thread

Barb shape alone doesn't make a thread good or bad. At your consultation, these are considered together.

• The direction you want to lift and how much sagging there is
• Skin thickness: barbs show through more easily in thin skin
• Number and placement of threads
• Whether there are hollow areas too: if lifting alone isn't enough, a separate plan for filling is needed