How Does the Body Heal a Wound?
The body heals a wound in a set order of steps. First it stops the bleeding, then it cleans the area, then it builds new tissue and new skin, and finally it makes the repair stronger. Most small wounds close within a few weeks, but the strengthening goes on quietly for a year or more.
By Chris Morais, MSc, MPhil, PhD
Published
A wound heals in four overlapping stages. A clot seals the injury, white blood cells clear germs and dead tissue, new tissue and skin grow to fill and cover the gap, and collagen is slowly rearranged to strengthen the repair. Deep wounds usually heal with a scar, which is never quite as strong as the original skin.
- What Are the Stages of Wound Healing?
- How Does the Body Stop Bleeding From a Wound?
- Why Does a Wound Become Red and Swollen While It Heals?
- How Does New Tissue Fill a Wound?
- How Does New Skin Cover a Wound?
- Why Do Healing Wounds Itch?
- How Does a Healed Wound Get Stronger Over Time?
- Why Do Wounds Leave Scars?
- What Makes a Wound Heal Slowly?
- Frequently Asked Questions
What Are the Stages of Wound Healing?
Wound healing has four main stages: stopping the bleeding, inflammation, rebuilding and strengthening. Each stage begins before the last one has fully ended, so they overlap.
The work starts within seconds of the injury. Blood begins to clot almost at once to stop blood loss[2]. Over the next few days, the immune system moves in to fight germs and clean the wound[2]. New tissue starts to form within about 2 to 10 days[3], and this building stage lasts for about 3 weeks in a typical wound[2]. The last stage, strengthening, starts at around 3 weeks and can go on for more than a year[3].
Smaller wounds heal faster than large or deep ones[2]. The way a wound is closed also matters. When the edges of a cut lie close together, as in a clean cut or a stitched wound, only a thin line of new tissue is needed. When the edges are far apart, the body must fill a much larger gap and then pull the edges closer together, which takes longer[1]. This is why doctors often recommend stitches for deeper cuts[1].
The table below shows what happens in each stage.
| Stage | When it happens | What the body does |
|---|---|---|
| Stopping the bleeding | Within minutes | Forms a clot that plugs the wound, which later dries into a scab |
| Inflammation | Mainly the first few days | Sends fluid and white blood cells to fight germs and clear dead tissue |
| Rebuilding | From a few days to about 3 weeks | Fills the gap with new tissue and blood vessels, and grows new skin over the top |
| Strengthening | From about 3 weeks to a year or more | Rearranges collagen to make the repair stronger, and the scar slowly fades |
For a broader look at how the body responds when tissue is hurt, see What Happens When Cells and Tissues Are Damaged?
How Does the Body Stop Bleeding From a Wound?
The body stops bleeding by forming a blood clot that plugs the damaged blood vessels. This process is called hemostasis.
First, tiny cell pieces in the blood called platelets stick to the damaged area and clump together. Then a protein called fibrin forms a mesh over the platelet plug[3]. This fibrin mesh traps blood cells and helps pull the edges of the wound together[1]. It also acts as a frame that repair cells can later crawl along[3].
As the clot dries at the surface, it becomes a scab. The scab helps keep germs out of the tissue underneath[1],[2]. Over the following days, the clot shrinks and is slowly broken down as new tissue takes its place[1].
Why Does a Wound Become Red and Swollen While It Heals?
A wound becomes red and swollen because the body sends extra blood, fluid and white blood cells to the injured area. This response is called inflammation, and in the first few days it is a normal part of healing.
Injured cells release chemical signals that widen the nearby blood vessels. The extra blood flow makes the area red and warm[1]. Cells called mast cells also release histamine, which makes the walls of small blood vessels leaky[1]. Fluid then seeps into the tissue and causes swelling[1]. The swollen tissue presses on nerve endings, and chemicals released by injured cells also activate pain nerves, which is why a fresh wound feels sore[1].
The leaky vessels let white blood cells pass from the blood into the wound[1]. These cells are part of the immune system. Neutrophils are among the first white blood cells to arrive[3]. They attack germs that entered through the broken skin. Larger white blood cells called macrophages follow. Macrophages clear away the fibrin, dead cells and other debris[3]. They also release growth factors, which are signals that tell other cells to start building new tissue and blood vessels[3]. In this way, macrophages help move the wound from the clean-up stage to the rebuilding stage.
In a wound that is healing well, redness and swelling settle after a few days. Redness, pain or swelling that gets worse instead of better can be a sign of infection[2].
Is Pus a Sign of Healing or Infection?
Pus is usually a sign of infection, not of normal healing. Pus is a thick fluid made of dead white blood cells and tissue fluid[1], and it builds up when white blood cells are fighting germs in the wound.
A small amount of clear fluid oozing from a new wound is normal, because it helps clean the area[2]. Yellow or green pus is different. Along with increasing redness or pain, it can mean the wound is infected[2]. Broken skin is one of the main ways germs get into the body, as explained in How Do Microbes Spread and Enter the Human Body?
An infected wound should be checked by a doctor or nurse. Treatment may include cleaning the wound, draining the pus, or antibiotics when the doctor decides they are needed. Treating an infection does not interfere with healing. It removes something that is holding healing back.
How Does New Tissue Fill a Wound?
New tissue fills a wound when cells from the surrounding tissue move in and build a fresh support structure, along with new blood vessels to feed it. This happens during the rebuilding stage, which starts within about 2 to 10 days of the injury[3].
The main builders are fibroblasts. These are cells found in connective tissue, the tissue that supports and holds other tissues together. Fibroblasts move into the wound from the nearby healthy tissue[1]. They make collagen, a tough protein that gives skin its strength, along with other materials that fill the space between cells[1],[3].
At the same time, new blood vessels grow into the wound from vessels at its edges[1],[3]. This growth of new blood vessels is called angiogenesis. New tissue needs a good blood supply to bring oxygen and nutrients, so this step is essential. Tumors use the same process to grow, as explained in Why Do Tumors Need New Blood Vessels? Angiogenesis Explained
Some fibroblasts change into cells called myofibroblasts, which can contract like muscle cells. They pull the edges of the wound toward each other, so the gap becomes smaller[3]. This pulling is most important in large, open wounds whose edges are far apart[1].
What Is Granulation Tissue?
Granulation tissue is the soft, new tissue that fills a healing wound from the bottom up. It is made mainly of fibroblasts, the collagen and other materials they produce, and many tiny new blood vessels[1],[3].
Because it is packed with small blood vessels, healthy granulation tissue looks red or pink and moist, with a bumpy surface. It bleeds easily if it is touched or rubbed. Granulation tissue is temporary. Over the following weeks, many of its small blood vessels disappear, and it is slowly replaced by firmer, paler tissue that becomes the scar[1].
How Does New Skin Cover a Wound?
New skin covers a wound when skin cells at the edges of the wound multiply and move across the gap until they meet in the middle. This step is called re-epithelialization.
The cells that do this work are keratinocytes, the main cells of the outer layer of the skin. They crawl in from the wound edges and divide to make more cells as they go[3]. They move across the surface of the new tissue underneath the scab. When the cells from all sides meet, they stop moving and build up into new layers of skin. Once the wound is sealed, germs can no longer enter it easily.
When the scab falls off, the new skin underneath may look stretched, red and shiny[2]. This is normal. It is thinner than the skin around it at first, and it slowly thickens and becomes more like the surrounding skin over the following weeks and months.
Why Do Healing Wounds Itch?
Healing wounds often itch because nerve endings in the skin react to chemicals released in the wound, such as histamine. Itching is a normal part of healing[2], although scientists still do not fully understand why wounds itch[4],[5].
The skin contains thin nerve fibers that carry itch signals to the brain. These fibers are sensitive to histamine, growth factors and other itch-causing chemicals that may be present in wounds[4]. Histamine is released by mast cells in the skin, and it acts directly on these itch nerves[4]. Itch is felt during both normal and slow healing[5]. Scientists think it probably comes from several causes acting together, including inflammation, changes in the structure of the healing skin, and germs on the wound surface[5].
Itching is especially common after burns. Studies have shown that as many as 87% of adults with burns report itching[4].
Scratching can make the problem worse. Scratching triggers more inflammation, which stimulates the nerves again and keeps the itch going[4]. It can also damage the new tissue and reopen the wound[4]. Picking at a scab can slow healing and make a scar more likely[2].
How Does a Healed Wound Get Stronger Over Time?
A healed wound gets stronger as the body slowly replaces and rearranges the collagen in the new tissue. This strengthening stage, called remodeling, begins about 3 weeks after the injury and can last for more than a year[3].
The first collagen laid down in a wound is a thinner, weaker type called type III collagen. Over about 6 to 12 months, it is gradually replaced by type I collagen[3], the stronger type found in normal skin. The early collagen fibers are also laid down in a random pattern[1]. During remodeling, the fibers are rearranged and linked more tightly together, which adds strength.
As this happens, the scar usually becomes flatter, softer and paler. It may fade a great deal, and this can take as long as 2 years[2]. Even so, a scar does not regain the full strength of the original skin. It stays less strong and less flexible than the skin around it[2].
Why Do Wounds Leave Scars?
Wounds leave scars because the body repairs deep damage by filling the gap with collagen-rich tissue, instead of rebuilding the original skin exactly. A scar is the result of this fast, practical repair.
There are two ways the body can repair tissue. In regeneration, the lost cells are replaced by new cells of the same type[1], so the tissue looks and works as it did before. In scarring, the gap is filled with repair tissue instead[1]. Very shallow wounds, which damage only the outer layer of the skin, can usually regenerate fully. Deeper wounds, which reach the lower layers of the skin, are more likely to leave a scar[2].
Scar tissue is different from normal skin in several ways. Its collagen is arranged differently. It also lacks some of the structures that normal skin contains. After a serious injury, hair follicles and skin glands, such as sweat glands, do not grow back in the scar[3]. This is why scars usually have no hair and do not sweat.
Sometimes the body makes too much scar tissue. This can happen when the building and breakdown of the wound's support material get out of balance[3]. The result can be a raised, thick scar. A raised scar that stays within the edges of the original wound is called a hypertrophic scar. A keloid is a raised scar that grows beyond the edges of the original wound. People with darker skin are more likely to develop keloids[2].
Whether a tissue regenerates or scars depends mainly on two things: whether its cells are able to divide, and whether its underlying support framework survives the injury. Skin cells divide often, so small, shallow injuries to the skin regenerate well. When damage is large or deep, the body fills the gap with scar tissue instead.
What Makes a Wound Heal Slowly?
A wound heals slowly when something interrupts one or more of the healing stages, most often infection, poor blood flow or a long-term health condition. Many factors can slow healing, including[2]:
- Infection. Germs in the wound keep the body stuck in the clean-up stage.
- Diabetes. High blood sugar and damage to small blood vessels can slow repair.
- Poor blood flow. Tissue needs blood to bring oxygen and nutrients for repair.
- Older age. Healing tends to be slower in older people.
- Obesity.
- Smoking.
- Heavy alcohol use.
- Stress.
- Certain medicines. These include corticosteroids, non-steroidal anti-inflammatory drugs (NSAIDs) and some chemotherapy drugs.
A wound that stays open far longer than expected is called a chronic wound. In chronic wounds, inflammation does not settle down as it should[3],[5]. The wound contains too many enzymes that break down proteins, compared with the substances that normally keep those enzymes in check, so new tissue is broken down as fast as it is made[3]. Germs can also form a biofilm, a slimy, protective layer on the wound surface, which makes infection harder to treat[3]. You can read more in What Is a Biofilm and Why Is It Difficult to Remove?
Some medicines on this list are important for treating serious conditions. A person should never stop a prescribed medicine because of a slow-healing wound without first talking to their doctor. The doctor can weigh the benefits of the medicine against its effect on healing and adjust treatment if needed. Any wound that is not getting better, or that shows signs of infection, should be checked by a doctor or nurse.
Frequently Asked Questions
How long does it take for a wound to heal? It depends on the size and depth of the wound. A small cut usually closes within days to a few weeks, because new tissue grows for about 3 weeks in a typical wound[2]. The scar that remains keeps getting stronger for more than a year[3], and it can take up to 2 years to fade[2]. Large or deep wounds, and wounds in people with conditions such as diabetes, take longer.
Should a wound be covered or left open to the air? A wound should generally be kept clean and covered while it heals[2]. A covering helps protect it from germs and from being bumped or rubbed. Follow any specific instructions from a doctor or nurse, especially for stitched or surgical wounds.
Is it bad to pick a scab? Yes. Picking at a scab can slow healing and make a scar more likely[2]. The scab protects the new tissue underneath from germs[2], and it falls off by itself once the skin below has healed.
Why does new skin look pink and shiny? New skin often looks pink, stretched and shiny after the scab comes off[2]. It is thinner than the surrounding skin, and the tissue underneath still has many small blood vessels. Both the color and the shine usually fade as the area matures over the following months.
When should a wound be checked by a doctor? A wound should be checked by a doctor if it shows signs of infection, such as increasing redness, increasing pain, yellow or green pus, or a lot of clear fluid[2]. Medical help is also needed if bleeding does not stop after 10 minutes of firm, direct pressure, if the edges of the wound turn black, if a fever lasts more than 4 hours, or if the wound opens up again[2].
Morais C. How Does the Body Heal a Wound? [Internet]. BiologyWithin.com; 2026 Oct 19. Available from: https://www.biologywithin.com/2026/10/how-body-heals-a-wound.html
- Betts JG, Young KA, Wise JA, Johnson E, Poe B, Kruse DH, Korol O, Johnson JE, Womble M, DeSaix P. 4.6 Tissue Injury and Aging. Anatomy and Physiology 2e. OpenStax; 2022.
- National Library of Medicine. How wounds heal. MedlinePlus Medical Encyclopedia.
- Tottoli EM, Dorati R, Genta I, Chiesa E, Pisani S, Conti B. Skin Wound Healing Process and New Emerging Technologies for Skin Wound Care and Regeneration. Pharmaceutics. 2020;12(8):735.
- Paul JC. Wound pruritus: pathophysiology and management. Chronic Wound Care Management and Research. 2015;2:119-127.
- Papanikolaou M, Paul J, Nattkemper LA, Kirsner RS, Yosipovitch G. Prevalence and Mechanisms of Itch in Chronic Wounds: A Narrative Review. Journal of Clinical Medicine. 2025;14(9):2877.
Note on External Links: External links were checked and accessible when this article was published. Their content and availability may change over time and are outside the control of BiologyWithin.com.
Disclaimer: This article is for general educational purposes only and does not constitute medical advice, diagnosis, or treatment. Consult a qualified healthcare professional about personal health concerns.
.webp)
