When a child gets a cut, they might cry at first, but within just a few days, the wound typically scabs over and heals, with new skin growing back. But why do older adults, compared to healthy children, experience much slower healing when their bodies are injured? The answer lies in aging. Years of living can slow down the body's ability to heal most tissues, and skin wounds might offer researchers a “window” to understand why aging leads to slower recovery.
Wound healing is classically divided into three stages. The first is the inflammatory stage, where the body works to clean the wound. During this phase, macrophages enter the wound, killing bacteria and removing dead cells and debris. This clears the path for the next phase, proliferation, in which various processes come together to promote the regrowth of damaged skin. As the cells at the wound edges divide, new skin cells are formed, and fibroblasts lay down a supportive structure called the extracellular matrix, which holds the new cells together. Additionally, structures such as blood vessels, which supply oxygen and nutrients, need to regrow to support the healing process. This second phase effectively closes the wound and restores the skin's protective barrier.
The remodeling phase is the final stage, which can take several years. During this time, the newly formed skin is strengthened through several processes, and the initially disorganized extracellular matrix is replaced with a more durable structure. Any cells that are no longer needed, such as immune cells or fibroblasts, either become inactive or die. This is also why scars fade over time as the tissue strengthens.
Aging can disrupt the orderly and effective progress of these stages, particularly through age-related diseases that cause health problems. One such disease is diabetes, which is commonly seen in older adults. One of the ways diabetes negatively affects healing is by narrowing blood vessels, leading to poor circulation. Without adequate blood flow, vital nutrients and oxygen cannot reach the wound, preventing the second phase of healing from proceeding properly. Diabetes is just one of many age-related conditions that can interfere with the body's normal physiological processes, including wound healing.
Beyond diseases related to aging, cells themselves also age. In the aging process, cells lose the ability to divide and replicate. As people age, senescent cells accumulate in the skin and other organs, causing a variety of issues. When cell division slows or stops due to aging, the skin becomes thinner, and fat cells that cushion the skin decrease. This makes older skin more vulnerable to injury. Once the skin is damaged, it has a harder time healing, and aging immune cells become less effective at warding off bacterial infections, increasing the risk of severe skin infections.
In the regeneration phase, the slow rate of cell division results in delayed skin regeneration. But senescent cells aren’t just passive observers; they release toxic byproducts that damage surrounding tissue and trigger inflammation—even in the absence of bacterial threats. Some of these byproducts can even accelerate the aging of nearby cells, suggesting that cellular aging might be, in essence, contagious. These cells promote inflammation and drive a destructive cycle of tissue damage that further hinders successful regeneration and healing.
While the skin is the most visible organ, it offers researchers a window into understanding why healing slows as people age. However, any tissue in the body can be affected by aging, whether the damage is minor and accumulative over time (like the effects of smoking on the lungs), or discrete and dramatic (such as the death of heart cells during a heart attack). Different tissues may heal in various ways, but all tissues are similarly sensitive to the impacts of an aging immune system and declining regenerative capacity.
Understanding why healing slows down as we age is crucial. Currently, treatments for wounds are outdated and often ineffective. Some available methods include changing wound dressings, using antibiotics when infections occur, or providing hyperbaric oxygen therapy to improve circulation in diabetic patients. However, as scientists gain a deeper understanding of the aging process, new treatments may emerge. For example, neutralizing senescent cells in mice has already shown promise in improving a variety of age-related diseases. While the “elixir of youth” is still a long way off, researchers believe that future clinical therapies could help reverse aging, allowing skin and other organs to heal more effectively and quickly.
