Overview
When the skin is injured, the body starts a carefully ordered sequence of events to stop bleeding, fight infection, rebuild tissue and restore strength. In most people, a small cut is closed within days.
But when circulation is poor, blood sugar is high, or pressure and swelling persist, that sequence can stall. The result is achronic wound: one that hasn’t made meaningful progress in about four weeks, or hasn’t healed in three months.
Stages of healing
Every wound heals through four overlapping stages, and each one has its own needs.
Stage 1
Hemostasis
Minutes to hours
What happens
Blood vessels constrict and platelets form a clot, held together by a protein net called fibrin.
What the wound needs
A clean wound and controlled bleeding.
Stage 2
Inflammation
Days 1 to 6
What happens
Immune cells arrive to clear debris and bacteria and release growth factors. Chronic wounds often stall here.
What the wound needs
Oxygen for immune cells to kill bacteria; removal of dead tissue and excess fluid.
Stage 3
Rebuilding (proliferation)
Days 4 to 24
What happens
New tissue, collagen and blood vessels fill the wound, and skin cells begin to close it.
What the wound needs
Oxygen and nutrients for collagen and new vessels; a moist, protected wound bed.
Stage 4
Remodeling
3 weeks to 2 years
What happens
Collagen reorganizes and the area gains strength, reaching about 80% of its original strength.
What the wound needs
Protection from pressure and re-injury.
Timeframes are typical for an acute wound; chronic wounds can take much longer.
Why chronic wounds stall
Chronic wounds rarely have a single cause. Most are held back by several problems at once:
- Poor blood flow limits the oxygen and nutrients that reach the wound.
- Excess fluid and swelling damage surrounding skin and dilute the body’s repair signals.
- Infection and biofilm keep the wound in a constant state of inflammation.
- Pressure or friction keeps re-injuring tissue that is trying to heal.
- Underlying conditions such as diabetes slow the immune response and tissue repair.
The role of oxygen
Almost every step of repair consumes oxygen. In a healthy wound it arrives through the bloodstream. But poor circulation, diabetes, swelling and pressure damage can leave wound tissue low in oxygen (hypoxic), and hypoxic wounds tend to heal slowly or stall.
Fighting infection
White blood cells use oxygen to destroy bacteria.
Building collagen
Cells need oxygen to make strong, stable collagen, the scaffolding of new tissue.
Growing blood vessels
Oxygen signals help new capillaries form and supply the healing area.
Closing the surface
Skin cells need energy, and therefore oxygen, to migrate across the wound.
Clinicians have several ways to improve oxygen at the wound, from treating blocked arteries to oxygen therapies. Evidence for giving oxygen directly to the wound surface has grown, and the International Working Group on the Diabetic Foot (IWGDF) 2023 guidelines suggest considering it alongside standard care for diabetic foot ulcers that are not healing.
Managing fluid and pressure
Wounds produce fluid as part of healing, but too much of it softens and breaks down surrounding skin and keeps the wound inflamed. Controlling that fluid, and the swelling that comes with it, is a central part of wound care.
Negative pressure wound therapy
One well-established approach is negative pressure wound therapy, sometimes called a “wound vac.” A sealed dressing is connected to gentle, controlled suction. It has been used in hospitals and homes since the 1990s and can:
- Removes excess fluid (exudate) that can slow healing.
- Reduces swelling around the wound.
- Helps draw the wound edges together.
- Encourages healthy new tissue (granulation tissue) to form.
- Keeps the wound covered and sealed from the outside environment.
Principles of good wound care
Whatever the wound type, effective care tends to follow the same core principles.
Clean the wound bed
Removing dead tissue and debris (debridement) gives healthy tissue a chance to grow.
Control infection
Bacteria and biofilm keep a wound inflamed. Treating infection is often the first step.
Balance moisture
A wound heals best when it is moist but not wet. Too much or too little fluid both slow repair.
Restore blood flow and oxygen
Improving circulation, and in some cases giving oxygen to the wound, supports every stage of healing.
Relieve pressure
Offloading for foot ulcers, repositioning for pressure injuries and compression for venous ulcers address the cause.
Treat the whole person
Blood sugar control, nutrition and stopping smoking all affect how quickly a wound heals.
Resources
- Chen P, et al. Guidelines on interventions to enhance healing of foot ulcers in people with diabetes (IWGDF 2023 update). Diabetes Metab Res Rev. 2024.
- MedlinePlus (U.S. National Library of Medicine): How wounds heal
- Cleveland Clinic: Negative Pressure Wound Therapy
- Johns Hopkins Medicine: Vacuum-Assisted Closure of a Wound