How do wounds, cuts, scrapes, lacerations heal?


I fell on my roller blades yesterday and skinned my knee. Now I'm watching my knee change and I am fascinated by the healing process. Could you explain to me just what is happening?


Dear Reader,

Fascinating is a good word for healing — before you finished picking yourself up and brushing the gravel out of your knee, your body had already begun a complex process that'll soon have you ready to blade again (perhaps with knee pads this time?). This process involves processes within your blood vessels, blood cells, and skin cells working together to stop the bleeding, prevent infection, and heal the skin. 

The moment you cut or tear a blood vessel, the body's healing actors spring into action. Here's how healing works:

  1. The blood vessels leading to the wound tighten to reduce the flow of blood to the injured area, causing vasoconstriction.
  2. Platelets (triggered by enzymes leaked from the torn blood vessel) rush to the scene. These sticky blood cells clump to each other and then adhere to the sides of the torn blood vessel, making a plug.
  3. Clotting proteins in the blood join forces to form a fibrin net that holds the platelet plug in place over the tear, and in just a few seconds or minutes (depending on how bad the scrape is), bleeding stops, thanks to coagulation! The fibrin plug becomes a scab that will eventually fall off or be reabsorbed into the body once healing is complete.

Once bleeding has been controlled, the next step is stopping infection. The blood vessels that were constricted now dilate to bring white blood cells rushing to the scene. White blood cells engulf and destroy any germs that may have gotten into the body through the open wound. You might be able to see part of this immune response first hand if your wound appears pink or red, and slightly swollen. It might also be tender to the touch. This swelling happens due to the extra blood cells being brought to heal the wound, and is part of the natural healing process. 

When the enemies of blood loss and infection have been vanquished, the body turns its attention to healing and rebuilding:

  • Fibroblasts (cells that are capable of forming skin and other tissue) gather at the site of injury and begin to produce collagen, which will eventually fill in the wound under the scab and create new capillaries to bring oxygen-rich blood to the recovering wound.
  • Skin along the edges of the wound becomes thicker and then gradually migrates (or stretches) under the scab to the center of the wound, where it meets skin from the other side and forms a scar (about three weeks after the initial injury).
  • Scar tissue will become stronger and fade gradually over the next several years as more collagen is added but will only have about 80 percent of the strength of the original skin.

You may have noticed that not all wounds heal equally. There are many different types of wounds, including cuts and scrapes, like your own, which are generally more minor, or puncture wounds, burns, or sores. Generally speaking, deeper, more serious wounds take longer to heal, and can affect body parts below the skin, such as muscles, nerves, blood vessels, or bones. Health care providers use specific classification methods to decide how serious a wound is by examining its properties, such as the size, depth, time since the injury, and color, and deciding whether or not it's infected (and to what degree). These classifications determine the type of treatment, which could involve cleaning the wound, repairing damaged tissue, prescribing antibiotics to kill bacteria, or administering a tetanus shot.

Acute wounds, which are recent injuries expected to undergo a natural healing process, can also become chronic wounds if they don't close over in a timely manner. Chronic wounds remain in a stalled state of healing, which may require extra medical care from a healthcare provider. Chronic wounds can develop due to many factors, from a lack of blood flow to the wound site, infections or pre-existing medical conditions, medications, nutrition deficiencies, or excessive pressure on the wound. If a wound becomes chronic, healthcare providers will examine and try to correct underlying factors such as these to promote wound healing. 

 Individual factors also influence how quickly your body is able to recover from a wound, including:

  • Age: Young people usually heal faster than older folks.
  • Nutrition: The body needs a good supply of vitamin C to make collagen.
  • Smoking or heavy drinking: Smoking and alcohol can both slow wound healing and increase the chances of infection.
  • Stress: Large amounts of stress can delay the healing process.
  • Other infections or illnesses: Diabetes, thyroid disease, and high blood pressure, for example, can decrease the body's ability to heal.
  • Clogged arteries: This can cause poor blood flow to the wound and slow healing.
  • Medications: Certain drugs including chemotherapy treatments, corticosteroids or nonsteroidal anti-inflammatory drugs (NSAIDs) can interfere with wound healing.

It can be hard to determine how severe your own injury may be, considering all of the complex factors at play, and that the full extent of a wound may not be visible at the surface of the skin. If you have a wound that's slow to heal, speaking with a health care provider can help to clarify the type of wound that you have and the best treatment option for you. 

Best of luck staying on your feet next time,

Last updated Aug 05, 2022
Originally published Sep 28, 2001

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