How Il 31 Causes Chronic Itching And Inflammation?

Itching that will not stop is exhausting. For millions of people with chronic skin conditions like eczema, the urge to scratch is relentless and can disrupt sleep, work, and daily life. The driver behind this constant itch is often a specific immune system protein called interleukin-31, or IL-31. This signaling molecule directly activates nerve fibers in the skin, sending an intense “itch” signal straight to the brain. At the same time, IL-31 promotes inflammation by recruiting other immune cells to the skin, creating a cycle of damage and further irritation that is difficult to break.

What Exactly Is IL-31?

IL-31 is a cytokine. Cytokines are small proteins that act as messengers between cells, particularly in the immune system. They tell other cells what to do. IL-31 is produced mainly by a type of immune cell called a Th2 cell. These cells are heavily involved in allergic reactions and in defending against parasites.

In healthy skin, IL-31 levels are low. In chronic inflammatory skin conditions, especially atopic dermatitis (eczema), IL-31 levels are significantly elevated. The higher the level of IL-31 in the skin, the more severe the itching tends to be. This link is so strong that IL-31 is now considered a primary driver of itch in these conditions.

IL-31 does not act alone. It binds to a specific receptor on the surface of cells, called the IL-31 receptor A. This receptor is found in high numbers on sensory neurons in the skin. These are the nerve endings that detect itch and pain. This direct connection between the immune system and the nervous system is why IL-31 is such a powerful itch trigger.

How Does IL-31 Trigger the Itch Signal?

The process begins when IL-31 attaches to its receptor on a nerve fiber in the skin. This binding sets off a cascade of signals inside the nerve cell. The nerve becomes activated and fires an electrical signal. That signal travels up the spinal cord and into the brain, where it is perceived as an itch.

This is not a slow process. The nerve activation happens quickly after IL-31 binds. Studies have shown that injecting IL-31 into the skin of animals or humans causes rapid and intense scratching behavior. This confirms that IL-31 is not just a marker of inflammation; it is an active and direct cause of the itch sensation.

IL-31 also makes nerves more sensitive. This means that after IL-31 exposure, even mild stimuli that would not normally cause itching can trigger a strong itch response. This heightened sensitivity is part of why chronic itch is so hard to manage. The skin becomes primed to itch at the slightest provocation, such as a change in temperature or the touch of clothing.

How Does IL-31 Drive Skin Inflammation?

Beyond the nervous system, IL-31 has direct effects on skin cells. It acts on keratinocytes, which are the main cells that make up the outer layer of the skin. When IL-31 activates these cells, it triggers them to produce more inflammatory chemicals.

This creates a feedback loop. The initial inflammation attracts more immune cells to the area. Those cells produce more IL-31. The higher IL-31 levels cause more inflammation and more itching. The scratching itself damages the skin barrier, which releases more inflammatory signals. This cycle is central to chronic conditions like eczema.

The inflammation caused by IL-31 also disrupts the skin barrier. A healthy skin barrier keeps moisture in and irritants out. When IL-31-driven inflammation damages this barrier, the skin becomes dry, cracked, and more vulnerable to infections. This explains why areas of chronic scratching often become thickened, leathery, and prone to bacterial colonization.

What Conditions Are Linked to High IL-31 Levels?

Atopic dermatitis is the most well-studied condition linked to IL-31. Research consistently shows that people with eczema have much higher levels of IL-31 in their skin and blood compared to people without the condition. The level of IL-31 correlates with disease severity.

IL-31 is also implicated in other itchy conditions. These include prurigo nodularis, a condition characterized by hard, intensely itchy bumps on the skin. It is also elevated in some cases of chronic spontaneous urticaria (chronic hives) and in certain types of cutaneous T-cell lymphoma, a rare form of skin cancer that causes severe itching.

It is important to note that IL-31 is not the only cause of itching in these conditions. Other cytokines and inflammatory mediators also play a role. However, IL-31 appears to be a particularly important and specific driver of the itch component, which makes it a valuable target for treatment.

How Is IL-31 Targeted by New Treatments?

Because IL-31 is so central to chronic itch, it has become a major target for drug development. The goal is to block the interaction between IL-31 and its receptor, stopping the itch signal before it starts.

One approach is a monoclonal antibody that binds to the IL-31 receptor. By occupying the receptor, the antibody prevents IL-31 from attaching to it. Clinical trials have shown that this approach significantly reduces itching in people with moderate-to-severe atopic dermatitis. Many patients report a noticeable reduction in itch within a few weeks of starting treatment.

Another approach involves blocking IL-31 directly. This means using an antibody that attaches to the IL-31 protein itself, neutralizing it before it can reach the receptor. This strategy is also being investigated and has shown promise in clinical trials for conditions like prurigo nodularis.

These targeted therapies represent a shift from broad immunosuppressants, which affect the entire immune system, to more precise treatments that address a specific driver of disease. The evidence for their effectiveness is strongest for atopic dermatitis, where they have been shown to improve both itch and skin clearance.

Are There Natural Ways to Reduce IL-31?

There is no natural supplement that has been proven to directly lower IL-31 levels in humans. Claims that certain herbs or vitamins can “block” this cytokine are not supported by clinical evidence. Be cautious of any product that makes such promises.

That said, managing the underlying condition can reduce IL-31 levels indirectly. When eczema is well-controlled, IL-31 levels in the skin tend to drop. This means that standard eczema treatments, such as topical corticosteroids, calcineurin inhibitors, and moisturizers, can help lower IL-31 by reducing the overall inflammatory environment.

Some lifestyle factors may influence itch severity, though their effect on IL-31 specifically is not well studied. Avoiding known triggers, such as allergens or harsh soaps, can prevent flare-ups. Keeping the skin well-moisturized supports the skin barrier and may reduce the signals that drive Th2 cell activity. These measures are helpful for overall disease management, but they should not be viewed as specific IL-31 inhibitors.

What Is the Difference Between IL-31 and Histamine?

Histamine is the classic itch mediator associated with allergies. It is released by mast cells and causes hives and itching. Antihistamines work well for this type of itch.

IL-31 acts through a completely different pathway. It does not require histamine to cause itching. This is a critical distinction because it explains why antihistamines often fail to relieve itching in eczema and other chronic inflammatory conditions. The itch in eczema is largely driven by IL-31 and related cytokines, not by histamine.

This difference also explains why the itch in eczema feels different from the itch of an allergic reaction. Eczema itch is often described as deep and persistent, while histamine-driven itch is more sudden and sharp. Understanding this distinction helps explain why a treatment that works for one type of itch may do nothing for another.

Can IL-31 Levels Be Measured?

IL-31 can be measured in research settings using blood tests or skin biopsies. However, this is not a routine clinical test. Doctors do not typically order IL-31 levels to diagnose eczema or to monitor treatment.

The diagnosis of conditions like atopic dermatitis is based on clinical examination and medical history. A doctor looks at the pattern of the rash, its location, and the patient’s symptoms. IL-31 measurement is primarily a research tool used to understand disease mechanisms and to evaluate the effectiveness of new drugs in clinical trials.

For patients, knowing about IL-31 is more useful for understanding why their itch happens and why certain treatments are recommended. It provides a biological explanation for a frustrating symptom and helps clarify why newer targeted therapies are designed the way they are.