I recently visited an 83-year-old patient in the hospital after EMTs rushed her to the ER with an infected leg wound. Her ordeal started inconspicuously when she bumped into the sharp edge of a table and developed a small cut. The patient’s wound didn’t close, but she ignored it until she woke up in pain one morning two weeks after first injuring her leg. Her daughter called 911 after noticing angry, red skin discoloration and pus – both signs of an infection. Our medical team treated her with IV antibiotics and cleared up the infection, but the wound did not fully close until at least a month later, well after she was discharged from the hospital.
How different the story is when children get a cut. They may scream initially, but within days, the scab falls off, revealing new skin. Why was healing so delayed in my 83-year-old patient compared to a healthy child?
The answer is age. Decades of life slow down healing for most tissues, and wounds in skin can offer a window into why this slowdown occurs.
Three stages of wound healing
I am physician who studies how aging predisposes patients to diseases like diabetes and whether behavioral changes such as intermittent fasting may slow down aging. In order to understand why the skin wound in my older patient healed so slowly, it is important to first understand how wounds heal under the ideal conditions of youth.
The wound healing process is classically categorized into three stages.
sInflammation sets the stage for the regenerative phase, where several processes work in concert to regrow damaged skin. Replacement skin cells are born when cells at the edge of the wound divide, while fibroblast cells lay down a supportive scaffolding called the extracellular matrix. This holds the new cells together. Any damaged supporting structures of the skin, such as the blood vessels that supply critical oxygen and nutrients, also need to regrow. The second stage effectively closes the wound and restores a protective barrier against bacteria.The first stage is inflammation, essentially the body’s attempt to clean the wound. During the inflammatory phase, immune cells called phagocytes move into the wound, kill any contaminating bacteria, and ingest and dispose of dead cells and debris.
The regenerative phase is a relatively quick, but tenuous fix – new skin is fragile. The final remodeling phase plays out over a couple of years as the new skin is progressively strengthened by several parallel processes. The extracellular matrix, which was initially laid down in a haphazard fashion, is broken down and replaced in a more durable way. Any residual cells from prior phases that are no longer needed – such as immune cells or fibroblasts – become inactive or die. In addition to strengthening the new skin, these collective actions also account for the tendency of scars to visibly fade with time.