Sutures are medical threads used to stitch wounds or surgical incisions closed, holding the edges of skin and tissue together while the body heals. They remain the standard method for wound closure in medicine, used in everything from minor cuts to major surgeries. Sutures work by bringing wound edges into direct contact, which allows new skin cells and connective tissue to bridge the gap, lowering infection risk and producing a cleaner scar than if the wound healed on its own.
How Sutures Help Wounds Heal
When a wound is stitched closed, healing happens through what’s called “primary intention.” Instead of the body slowly filling in an open gap with scar tissue (which takes longer and leaves a wider mark), the wound edges are held flush against each other. New skin cells grow across the narrow seam while connective tissue forms underneath for strength. This process results in faster healing, lower infection rates, and a thinner scar.
The three main goals of suturing are stopping bleeding, preventing infection, and producing a good cosmetic result. Different wounds call for different approaches depending on depth, location, and how much tension the surrounding skin is under.
Absorbable vs. Non-Absorbable Sutures
The most fundamental distinction between suture types is whether they dissolve on their own or need to be physically removed.
Absorbable sutures break down inside the body through a chemical process called hydrolysis. They’re used for internal layers of tissue, such as muscle or fat beneath the skin, where going back in to remove stitches would be impractical. Different materials dissolve at different rates. One common synthetic material loses about 60% of its holding strength after 21 days and fully dissolves within 56 to 70 days. A faster-dissolving version of the same material falls away on its own within 12 to 14 days, making it useful for the inside of the mouth.
Non-absorbable sutures are made from materials the body’s chemistry cannot break down, such as nylon or polypropylene. They provide long-lasting strength and are the standard choice for closing skin on the outside of the body. Because they won’t dissolve, they require a follow-up visit for removal.
Natural suture materials include silk and catgut (which, despite the name, is made from sheep intestine). Catgut can be treated with chemicals to make it stronger and slower to absorb. Most modern sutures, though, are synthetic because their strength and absorption rates are more predictable.
Monofilament vs. Braided Structure
Beyond the material itself, sutures differ in their physical structure. A monofilament suture is a single smooth strand, like a fishing line. A braided suture is made of many tiny fibers woven together, similar to rope.
Braided sutures are easier to handle and hold knots more securely, which is why surgeons still use them frequently. The tradeoff is infection risk. Bacteria cling more tightly to braided sutures because the grooves between woven fibers create hiding spots. Lab imaging has shown substantial bacterial growth in the grooves of braided material even after multiple washes, while smooth monofilament sutures of the same size showed far less contamination. For contaminated or high-risk wounds, monofilament sutures are the safer choice.
Common Stitching Techniques
Sutures can be placed in different patterns depending on the wound. The two broad categories are interrupted and continuous stitching.
Interrupted sutures are individual stitches, each tied and cut separately. This gives the surgeon precise control over spacing and tension at every point along the wound. If one stitch fails or becomes infected, the rest stay intact. Interrupted stitches generally produce good cosmetic results because each one can be adjusted independently to align the wound edges precisely.
Continuous sutures use a single thread running the length of the wound, like a sewing machine stitch. They’re faster to place and distribute tension evenly. A meta-analysis of randomized trials found that continuous sutures placed just beneath the skin surface scored higher in cosmetic appearance ratings from both patients and doctors compared to interrupted stitches. These under-the-skin continuous sutures also had significantly lower rates of wound reopening, particularly in high-tension areas like the abdomen, scalp, and limbs. Because the thread stays below the surface, it leaves no puncture marks on the outer skin.
For deeper wounds, a mattress stitch penetrates further into the tissue layers, providing more strength and reducing tension on the wound edges. Infection rates between continuous and interrupted methods are similar.
Suture Sizing
Sutures are sized using a standardized system regulated by the U.S. Pharmacopeia. The numbering works somewhat counterintuitively: the more zeros in the size, the thinner the thread. A 2-0 suture is thicker than a 4-0, which is thicker than a 6-0. Delicate areas like the face use very fine sutures (5-0 or 6-0) to minimize scarring, while areas under more stress, like the torso or joints, use thicker material.
Needle Shapes and Their Purpose
Every suture comes attached to a needle, and the needle’s shape matters as much as the thread. Cutting needles have a sharp triangular edge designed to pierce tough tissue like skin. Tapered needles have a smooth, rounded point that spreads tissue apart rather than slicing through it, making them ideal for delicate internal structures like blood vessels or intestines where tearing is a concern. Reverse cutting needles position the sharp edge on the outer curve, which reduces the chance of sutures ripping through soft tissue.
Barbed Sutures
A newer development is the barbed suture, which has tiny angled cuts along the thread that grip tissue like fish hooks. This design eliminates the need for knots entirely. The barbs anchor the suture at multiple points along the wound, distributing tension more evenly across a larger area. In laparoscopic (keyhole) surgery, where tying knots through small incisions is technically difficult, barbed sutures have been a significant advancement. Studies in surgical models show they cut closure time roughly in half compared to interrupted stitches and create a stronger seal. Because there are no knots, they may also provoke less inflammation in the surrounding tissue.
When Sutures Come Out
Non-absorbable sutures need to be removed once the wound has healed enough to hold itself together. Timing depends on location, because different parts of the body heal at different speeds:
- Face: 4 to 5 days
- Scalp: 7 to 10 days
- Arms and backs of hands: 7 days
- Chest, abdomen, or back: 7 to 10 days
- Legs and tops of feet: 10 days
Facial sutures come out earliest because the face has excellent blood supply and heals quickly. Leaving sutures in too long increases the risk of visible “track marks” on either side of the scar. Removing them too early risks the wound reopening.
Signs of Complications
Most sutured wounds heal without problems, but there are a few things to watch for. Wound dehiscence, where the incision reopens, is the most concerning complication. Warning signs include bleeding from the site, broken stitches, fever, increasing pain, swelling, redness or darkening of the surrounding skin, and a pulling or ripping sensation at the incision. Infection is the most common cause of wound reopening, though severe coughing or vomiting after surgery can also put enough pressure on stitches to cause them to fail.
A stitch abscess, a small pimple-like bump at the suture site, can occur when the body reacts to the thread material or when bacteria enter along the stitch track. Braided sutures and knots are more likely to trigger this kind of reaction than smooth, knotless alternatives.