Trained in dentistry, Sree is currently pursuing lab sciences. She loves researching and sharing information on various health topics.
Sometimes, you just have the worst luck. You're cutting up vegetables for dinner, and the knife slips and cuts your hand. You're running along a dirt road and you trip and fall, and scrape one or both of your knees. You're hitting that speed bag, and at the end of it you take off your gloves and discover that you've busted your knuckles open. Nothing to do for it but bandage up that wound and wait for it to heal, right?
The problem is, sometimes a wound that's still healing can drive you crazy. So let's find out: Why do cuts itch?
The Process of Wound Healing
The human body is capable of great feats of recovery. If a bone is broken, it can knit the separated ends back together. If an infection sets in, it can deploy various defenses to stop the infection in its tracks. Given enough time and the correct treatment or sequence of treatments, it can even bounce back from certain systemic dysfunctions.
The speed at which the body recovers from an injury depends on the kind of injury that the body suffers. In the case of a wound, the body suffers a sharp injury which causes damage to at least one layer of the skin. Wounds can be divided into two broad types, as shown in the table below.
An open wound is any kind of wound that breaks at least the epidermis, which is the outermost layer of the skin. Deep open wounds affect not only the epidermis, but also the dermis, which contains nerves and nerve endings, as well as hair follicles, sweat glands, and sebaceous glands. And some open wounds go all the way down to the subcutaneous tissue, which is primarily used for fat storage.
On the other hand, a closed wound is characterized by internal bleeding that affects interstitial tissues. When the closed wound primarily affects the dermis and/or the subcutaneous tissue, then it is informally referred to as a bruise. A closed wound usually results from blunt force trauma that breaks the blood vessels beneath the skin, but does not cause the top layer of the skin to break open.
As soon as the body perceives that it's been wounded, it starts with the process of wound healing. This process is divided into several predictable and commonly recognized phases. Understanding this healing process can help you to understand the reasons why do cuts itch.
|Type of Wound||Examples||Layer(s) of Skin Affected|
Cut, tear, puncture wound
Contusion / bruise
Phases of Wound Healing
Phase One: Hemostasis
This phase is also known as the clotting phase. The goal of clotting, or coagulation, is to stop blood from flowing out of the site of the injury. During the clotting phase, the blood at the site of the injury is changed from a liquid to a gel-like state.
Hemostasis begins when the regular flow of blood comes into contact with collagen from the broken or injured dermis. This causes the platelets, blood cells whose sole purpose is to stop bleeding, to start aggregating at the site of the injury.
At the site, the platelets secrete inflammatory factors and express chemicals called glycoproteins that allow them to aggregate into a mass.
The strength of that mass is boosted by the collection and activation of the proteins fibrin and fibronectin. They work together to form a plug, which prevents further blood loss from the site of the injury.
Throughout this process, platelets continue to build up on and around that plug. In the later stages of the coagulation process, these cells secrete growth factors that stimulate cells to divide more rapidly, as well as inflammatory factors that cause cells to migrate to the site of the injury. Other substances released by the platelets also cause blood vessels to dilate, making it easier for white blood cells to reach the wound.
At this stage of the wound healing process, it might be because of the initial secretion of inflammatory factors.
Phase Two: Inflammation
Inflammation refers to swelling or reddening at the site of an injury -- and while most of the time we think of this as a problem, it's actually a necessary part of the wound healing process. During this phase, different types of white blood cells collect at the site of the initial injury.
By releasing free radicals, neutrophils consume debris and kill any bacteria present in the wound. They also play a role in cleaning up the wound, as they secrete proteases, which help to break down damaged cells and tissues.
Macrophages also consume bacteria and clean up damaged cells. They consume the spent white blood cells, and release other proteases. They also produce the factors that pave the way for angiogenesis, which is the process of growing and regenerating blood vessels.
Helper T cells secrete cytokines at the site of the injury. These substances keep the blood vessels around the area dilated as well as easily accessed by other white blood cells.
In the later stages of the inflammation phase, some open wounds might secrete pus. Properly referred to as an exudate, pus is a mixture of plasma, active and dead white blood cells, and broken-down cells from the original site of the injury. Bacteria that have entered the wound and that have been neutralized by the white blood cells during this phase of wound healing will also exit the body in the form of this exudate.
While inflammation is part of the process of wound healing, prolonged inflammation, or inflammation that is delayed in resolving, may result in tissue damage. The key is to keep inflammation to manageable levels.
During this phase, bacteria that have entered the wound might set off pathogenic reactions, including swelling, redness, and itching.
Phase Three: Growth of new tissue
This stage is also referred to as the proliferation stage. Here, the “cleaning” process that takes place during inflammation gives way to the regrowth and regeneration of damaged tissue and blood vessels.
In angiogenesis, cells from blood vessels already present near the site of the injury migrate to the site and begin to lay down the framework for new blood vessels. In time, these new blood vessels begin to reform the networks that were destroyed or damaged by the injury.
The other regrowth process that takes place at the same time as angiogenesis is fibroplasia. It is mediated by fibroblasts that travel to the site of the injury. These cells build up an extracellular matrix at the site, which is then used as scaffolding upon which to deposit new layers of collagen.
With the extracellular matrix and collagen in place, granulation tissue can form at the site of the wound. This type of tissue is characterized by densely-packed connective cells and networks of tiny blood vessels.
Too much granulation in open wounds can result in the tissue turning into lumps that protrude out over regular skin. These lumps are colloquially referred to as “proud flesh”.
When there is a sufficient amount of granulation tissue in place, the process of reepithelialization can begin. Keratinocytes are the primary cells involved in this step, and they are often accompanied by the various epithelial cells that will eventually differentiate into hair follicles, sweat glands, and sebaceous glands. These cells grow and multiply at the edges of the wound, and crawl forward to meet in the middle.
However, if the wound is deep enough to leave a significant scar, the keratinocytes will only be able to lay down new epithelial tissue. That new tissue will not have hair follicles, sweat glands, or new nerves.
The final stage deals with the contraction of the wound -- i. e., what is considered to be the process of “closing” it. Key to this stage is the myofibroblast, which contains actin. These cells link up with each other and congregate at the edges of the wound. Gradually, the actin in these myofibroblasts contracts, and this is what pulls the edges of the wound together. Collagen from fibroblasts eventually acts as the cement that completes the seal.
At this stage of the wound healing process, itching can be a natural consequence of the growth of new cells and new tissue.
Phase Four: Remodeling
During this stage of the wound healing process, a different type of collagen is laid down at the site where the injury was located. The fibers in this type of collagen are gradually interlinked and connected and aligned, following the tension lines in the skin. The remodeling process can take place over a year or even longer, depending on the original injury that was sustained.
This type of collagen is also responsible for the formation of scar tissue. Scars are a natural and mostly expected result of wound healing. Most types of wounds leave scars behind. The only difference is the amount of scarring involved, which varies from person to person and from injury to injury.
An overproduction of collagen in the scar tissue can result in a hypertrophic scar, which is raised above the surface of the surrounding skin. If the scar expands such that it encroaches on skin beyond the initial site of injury, it becomes a keloid scar.
If the scar takes the form of a sunken or pitted depression in the skin, it is referred to as an atrophic scar. These scars are caused by the loss of underlying structures such as muscle or fat.
Over the course of this stage, collagen fibers continue to grow and realign, which could result in itching.
Delays in the Wound Healing Process
The process of wound healing is complicated and fragile. It can easily be interrupted, or it can even fail altogether. When there are clear and marked delays in the wound healing process, the first thing to do is to look at which stage has been interrupted or delayed.
In the most general sense, doctors recommend keeping the site of the wound moist. In a moist environment, wounds heal more quickly, and the patient feels less pain. The moist environment can also lead to less scarring, or less prominent scarring.
During the hemostasis stage, a lack of platelets in the blood can result in an extended period of bleeding. Similarly, low production of fibrin and fibronectin can lead to delays in the clotting process.
Wound care is important, especially during the inflammation stage: cleaning all debris from the site of the injury will speed up the process and shorten the period of inflammation. However, there is no need to be too aggressive. Don't allow the wound to be reopened or aggravated.
A healthy immune system is key during the inflammation stage, as a compromised immune system will be unable to clear all debris and damaged tissue from the wound, or will take too long to do so. This could lead to a prolonged inflammation phase, or to the injury becoming a chronic wound.
As new tissue grows at the site of the injury, take care not to scrape away the scabs or any tissue overgrowths. Doing so might reopen the wound, resulting in the healing process becoming delayed, or having to start all over again.
Finally, just because a scar has formed over the site of the injury doesn't mean that the healing process has finished. In fact, the wound itself is still vulnerable to re-injury. It is entirely possible for the scar over a wound to be damaged, making it necessary to go through the entire healing process again.
Why Do Cuts Itch?
Let's go back to the example of the knife slipping while you were cutting vegetables for dinner. The first thing to do is to wash the cut area under cool running water -- but don't overdo it! Wash just long enough to get rid of any visible dirt or debris on the cut area. Then apply an adhesive bandage and go on with your day.
While it's hidden away from sight, your cut is already undergoing the process of wound healing. The blood stops flowing thanks to your platelets and coagulating factors, paving the way for the inflammation stage and further cleaning of the injured tissues.
Here's a question that you might need to ask during the inflammation stage: why do cuts itch? What causes that irritating itch in your cut, even when it's already supposed to be healing?
One possible culprit is histamine. This is an organic compound of nitrogen and hydrogen. Within the human body, histamine is produced and stored in mast cells, as well as in certain types of white blood cells. Mast cells tend to collect at places in the body where injuries are likely to occur, such as the nose, the mouth, and in blood vessels.
Histamine, of course, is the compound that is implicated in allergic reactions. An excess of histamine in the body, produced in response to the presence of airborne allergens or those present on the skin, can cause different symptoms such as sneezing or itching.
In the case of your cut: as soon as your body perceives that there was an injury, it starts releasing histamine from the mast cells and white blood cells near that injury. With histamine now present in the bloodstream, other white blood cells and proteins can pass more easily through the blood vessels closest to the cut, so that they can quickly fight off any infections that may arise. However, it is also the very presence of histamine that might be a reason as to why do cuts itch.
Another possible reason for why do cuts itch might be related to recent medical discoveries: in this case, the existence of specific nerves in the skin. Some nerves respond primarily to changes in temperature while others respond primarily to changes in pressure. It's recently been discovered that some nerves might respond primarily to stimulation by causing the brain to fire off an itching response.
Finally, the process of wound healing itself might make that cut feel itchy. This can happen in either of the later stages of the wound healing process: the proliferation stage, or the remodeling phase.
Itchiness can occur while new tissue is growing, because these new cells appear around the edges of the cut and multiply quickly. This causes the edges to pull together and then downwards -- in effect, the growth contracts to seal the cut closed. The new cells themselves provide the stress that causes the urge to scratch at the healing cut.
Near the end of the wound healing process, as previously mentioned, scar tissue grows over the site of the cut. If there is too much scar tissue, that might rub against clothing or, if the cut was on an exposed area of skin, against other surfaces. This is another possible reason as to why do cuts itch.
Don't Scratch That Itch!
That feeling of itchiness might well be a part of the wound healing process, but it can also be a distraction. But it's not a good idea to scratch that itchy cut, as that might pull away the scabs, introduce new bacteria or infectious agents to the healing wound, or reopen the cut.
Knowing the reasons and risk factors as to why do cuts itch certainly helps -- but here are some other suggestions to manage that itchy feeling:
- Use a moisturizer to rehydrate the skin surrounding the itchy cut. Dryness can make the skin feel irritated and itchy.
- Wash the cut and the skin surrounding it with warm water and a mild soap. Don't use hot water, as that might burn the still-regrowing skin. Rinse well and make sure that no soap is left on the wounded area, then pat dry with a soft towel. Don't rub the towel over the wound.
- Cover the cut with a cool or cold compress. You can use a gel pack or a bag of frozen peas, but make sure to wrap the pack or the bag in a clean dry towel first. Apply the compress for no more than 20 minutes at a time.
- Protect the cut from irritation caused by tight or non-breathable clothing. Wear loose, breathable clothes. Carefully blot off any sweat that might lodge in the area around the cut.
- Topical preparations such as antibiotic creams should be used only if your doctor recommends them. Your doctor will also give you advice as to what preparations you can use, and for how long.
- If necessary, cover the cut with a wound dressing. Ask your doctor to recommend the right type of dressing for your specific injury.
If the itchiness is accompanied by redness, swelling, or some other change in the appearance of the cut, or if you notice any odd smells or discharge coming from the area around the wound, consult a doctor immediately.
Caring for Closed Wounds
Bruises, too, can itch as they undergo the healing process, and treatment depends on the severity of the bruise.
For light bruises, a doctor might recommend RICE first of all. RICE stands for Rest, Ice, Compression, and Elevation. Follow these steps to reduce or, if you're lucky, completely prevent swelling. The ice and the elevation can restrict blood flow to the bruise and halt or bring down the internal bleeding, while resting can hasten the rate of recovery.
Oddly, a bruise that is at least three or four days old might respond to the application of a warm compress. The idea is that warming up the bruised area will increase the blood flow in the area, therefore encouraging the movement of healing factors to the bruise.
In most cases, bruises heal on their own -- though your skin might turn some rather interesting shades in the process. The colors are caused by the breakdown of the blood and blood vessels in the affected area. However, large or persistent bruises, or bruises located in critical organs such as the brain, may require surgical intervention to resolve completely. A doctor may puncture the bruise to let the blood that has accumulated in the affected area to exit.