Wound healing stages: what is normal and when to worry

Every cut, graze, surgical incision or ulcer goes through the same basic repair process. Knowing the stages helps you tell the difference between a wound that is quietly doing its job and one that needs a professional to look at it. This guide explains the four wound healing stages with typical timings, the signs of a healing wound, the red flags, why some wounds heal slowly, and where hyperbaric oxygen does and does not fit.

What are the four stages of wound healing?

Clinicians describe four overlapping phases. They blend into each other rather than switching on and off, and the timings below are typical rather than fixed.

1. Haemostasis: straight away

According to the StatPearls review of wound physiology, haemostasis begins immediately after injury. Blood vessels narrow, platelets clump together and a clot forms to control bleeding. That clot also acts as a temporary framework for the repair cells that follow.

2. Inflammation: the first several days

Over the first several days, immune cells move into the wound to clear debris and bacteria. Chemicals released in this phase widen local blood vessels and make them leakier, which helps cells reach the area. This is part of why a fresh wound can look pink and feel warm and a little swollen at first. The difference between this and infection is direction: normal inflammation settles over days, while infection gets worse.

3. Proliferation: roughly day 3 to day 21

StatPearls describes the proliferative phase as occurring 3 to 21 days after injury. New blood vessels grow, granulation tissue fills the gap, collagen is laid down and new skin creeps across the surface. The main job of this phase is filling the wound.

4. Remodelling: from about week 3, for up to a year

A companion review, Wound Healing Phases, says remodelling starts around week 3 and can last up to 12 months. Collagen is reorganised and the wound contracts. A wound regains about 80% of its original strength by 3 months, but never quite 100%. New scars are typically firm, slightly raised and red for the first 6 to 9 months before they soften, flatten and fade.

What are the signs of a healing wound?

A wound that is healing well usually shows steady, day-by-day progress:

• bleeding stops and a scab or covering forms
• early redness, warmth and swelling settle rather than spread
• pain eases over the days, rather than increasing
• the wound gets smaller as new tissue fills in from the edges
• the new scar is pink or red at first, then gradually fades over months

The NHS says most cuts and grazes can be treated at home and will start to heal in a few days. Surgical wounds usually take longer; Guy's and St Thomas' NHS Foundation Trust notes they usually heal 2 to 3 weeks after the operation.

What does a healing wound smell like?

There is no special smell that proves a wound is healing. What matters is change. Cambridge University Hospitals lists an unpleasant smell among the signs that a wound may be infected, alongside increasing pain, redness, swelling, and fluid, pus or blood leaking from it. The NHS also lists foul-smelling discharge as a possible symptom of a venous leg ulcer, which needs specialist treatment. If a wound starts to smell, get it checked rather than covering it up.

When should you get a wound checked?

Get urgent advice from NHS 111 or your GP if, according to the NHS:

• a cut is swollen, red and getting more painful, or pus is coming out of it
• you feel generally unwell or have a high temperature
• the wound has soil, pus or body fluids in it, or is still dirty after cleaning
• a cut is larger than around 5cm

Go to A&E or call 999 if bleeding will not stop, blood spurts out, you lose feeling near the wound, or the wound is very large or deep.

Call 999 for possible sepsis. The NHS sepsis page lists breathing very fast, confusion or slurred speech, blue, pale or blotchy skin, and a rash that does not fade when pressed.

See your GP about slow wounds. The NHS defines a leg ulcer as a sore that takes more than 2 weeks to heal and advises seeing a GP, as it needs specialist treatment. With compression therapy from a trained professional, most venous leg ulcers heal within 6 months.

If you have diabetes, take any foot wound seriously. NICE guideline NG19 says a foot ulcer with fever or any signs of sepsis needs immediate referral to acute services, and other active diabetic foot problems should be referred to a specialist foot service within 1 working day.

Why do some wounds heal slowly?

StatPearls says wounds generally heal in 4 to 6 weeks, and those that fail to heal within that time are classed as chronic. The reasons it lists fall into two groups.

Whole-body factors: diabetes, smoking and malnutrition. Diabetes raises the risk of small blood vessel disease, which reduces blood flow to the wound. Smoking narrows blood vessels and lowers the oxygen reaching the wound, and nicotine slows the cells that build new tissue.

Local factors: low oxygen or poor blood supply, infection, pressure on the area, swelling, a wound that is too wet or too dry, and bacterial biofilm, a protective slime that bacteria form and that can block healing cells and antibiotics.

This is why a slow wound needs an assessment of the cause, not simply a different dressing. Blood supply, infection, pressure relief and blood sugar control are the foundations. District nurses, practice nurses, podiatrists, tissue viability teams and vascular specialists are the people who manage them.

Where does hyperbaric oxygen fit?

Hyperbaric oxygen therapy (HBOT) means breathing concentrated oxygen in a pressurised chamber, which raises the amount of oxygen carried in the blood. Because low oxygen is one reason wounds stall, it has been studied as an addition to standard wound care.

• Recognised for selected wounds. The Undersea and Hyperbaric Medical Society includes "enhancement of healing in selected problem wounds" in its list of indications. The word selected matters.
• Short-term signal in diabetic foot ulcers. A 2015 Cochrane review found 10 trials with 531 participants. Pooled data from 5 trials (205 people) showed more ulcers healed at 6 weeks with HBOT, but the benefit was not evident at one year, and there was no significant difference in major amputation. The authors said flaws in the trials meant they were not confident in the results. Cochrane noted in 2020 that an update of this review was underway.
• Not routine in the NHS for diabetic foot ulcers. NICE NG19 says hyperbaric oxygen therapy should not be offered to treat diabetic foot ulcers unless as part of a clinical trial.

Our single-person chamber runs at 1.5 ATA, and we do not carry the results of hospital trials over as promises about treatment here. For some people with a difficult wound, HBOT may be worth discussing as a supporting option once circulation, infection, pressure relief and the underlying condition have been properly assessed. It never replaces the care your nurses, podiatrist or specialist team provide.

Our page on non-healing wounds explains how we think about that pathway. Before considering any session, read who HBOT is not suitable for and what hyperbaric oxygen therapy is. No referral needed. Medical consultation included.