Maybe it starts with a patch of itchy skin that just won’t go away. Or maybe the bumps slowly fade, only to pop back up in the same place next week. For some people, this type of experience marks the beginning of chronic (long-term) hives. This skin condition, also called chronic urticaria, can be uncomfortable, unpredictable, and hard to describe.

In this article, we’ll talk about possible causes of chronic hives. We’ll explain why they can be so difficult to pin down and share the most common triggers that lead to flare-ups. You’ll also learn why these itchy spots aren’t always caused by allergies and how the immune system may be involved.

Chronic Hives: A Brief Overview

Chronic hives are raised, itchy bumps or welts that keep coming back multiple times per week for more than six weeks. They can appear nearly anywhere on the body — arms, legs, face, chest — and may move from one area to another. They may vary in size and shape.

On light, olive, and tan skin tones, the hives may be red or pink. On darker skin tones, they can look purple, gray, or skin-colored. About 40 percent of people also develop angioedema. This is a deep and sometimes painful swelling under the skin that can affect the lips, eyelids, genitals, or hands.

Unlike acute (short-term) hives, which often appear after an allergic reaction and fade quickly on their own, chronic hives can last for months or even years. Studies estimate that as many as 5 percent of people will develop chronic hives at some point in their lives. Women ages 30 to 50 are at higher risk.

Causes and triggers can vary depending on the type of chronic hives you have. There are two main types of chronic hives:

• Chronic spontaneous urticaria or chronic idiopathic urticaria — “Idiopathic” means no clear cause. This type of chronic hives is more common, and it means that the hives appear without an obvious trigger or reason.
• Chronic inducible urticaria — This type occurs when chronic hives are caused by specific physical or environmental factors, such as heat or cold.

Why Chronic Hives Happen

Unfortunately, the exact cause of chronic hives isn’t fully clear. In some people, the body’s immune system releases a chemical called histamine, which causes small blood vessels in the skin to leak. This can lead to the itchy bumps and swelling that happen with hives.

Histamine is stored inside certain immune cells. When these cells are activated, they burst open and release histamine into nearby tissue. Normally, this process helps fight infection and heal injury. However, in chronic hives, it happens too often or without a reason.

Common Triggers of Chronic Hives

Even though the exact cause of chronic hives can be hard to find, certain factors trigger or worsen flare-ups. However, these triggers vary widely from person to person. Some are linked to how the immune system reacts, while others may come from physical or environmental factors.

Understanding these triggers can help you and your healthcare team identify patterns, reduce outbreaks, and choose the best treatment options.

Autoimmune Triggers

In many cases — possibly up to half — autoimmune activity is thought to play a major role. In autoimmune forms of chronic urticaria, the body mistakenly targets its own cells, making antibodies (immune proteins) that set off inflammation.

Autoimmune chronic hives are more common in people with conditions such as:

• Thyroid disease
• Type 1 diabetes
• Celiac disease
• Lupus
• Rheumatoid arthritis

Some studies suggest that people with certain autoimmune conditions may have higher levels of thyroid autoantibodies (antibodies that attack the body’s own cells) and decreased activity of other special immune cells called regulatory T cells. This mix of higher thyroid autoantibodies and lower levels of regulatory T cells may disrupt the immune system’s signaling and contribute to chronic hives.

Allergens and Sensitivities

While acute hives often follow a clear allergic reaction, chronic hives usually aren’t caused by allergies. Still, certain allergens or sensitivities can lead to chronic hives or make symptoms worse. Possible triggers include:

• Foods like shellfish, eggs, or nuts
• Food additives, such as preservatives or colorings
• Alcohol
• Certain over-the-counter medications, such as nonsteroidal anti-inflammatory drugs (NSAIDs)
• Environmental allergens, like pollen, dust, or pet dander
• Insect bites or stings

If you think allergies may be triggering your hives or making them worse, ask your doctor for a referral to an allergist.

Physical and Nonphysical Triggers

Certain physical factors can cause or make chronic inducible urticaria worse. These are the various types of chronic hives that have physical triggers:

• Cold urticaria — Triggered by exposure to cold air, wind, or water
• Heat urticaria — Caused by exposure to warmth or hot environments
• Delayed-pressure urticaria — Appears several hours after pressure on the skin, such as from tight straps or sitting for too long
• Dermographism — Raised lines or welts on areas where the skin is rubbed, scratched, or pressed, even lightly
• Solar urticaria — Develops after exposure to sunlight or ultraviolet rays
• Exercise-induced urticaria — Occurs after physical activity
• Vibratory urticaria — Triggered by vibrations from tools or machinery

In addition to these physical factors, some people react to less visible factors. Nonphysical types of triggers for chronic hives include:

• Aquagenic urticaria — Hives develop after direct contact with water, regardless of temperature.
• Cholinergic urticaria — Triggered when the body warms up from heat, stress, or sweating.
• Contact urticaria — Caused by skin contact with certain substances, such as fragrances, preservatives, metals, or certain foods.

Infections and Other Health Conditions

Infections are among the most common causes of acute hives, but in some cases, they can also lead to chronic hives. Viral or bacterial infections may activate the immune system, causing it to release histamine and trigger hives.

Chronic hives can also develop with other health conditions. One example is autoimmune vasculitis. In this condition, the blood vessels become inflamed, which can cause pain, swelling, or skin changes. Liver disease, lymphoma, and asthma have also been linked to chronic hives in some people.

Stress and Hormones

Stress usually doesn’t cause hives on its own, but it can certainly make them worse. Major life changes — like a death in the family, a new job, a divorce, or even a wedding — can trigger or prolong flare-ups. Emotional stress releases hormones that may increase inflammation and histamine activity in the skin. For some people, this creates a cycle of stress and hives that’s hard to break. Hormonal changes from menstruation, pregnancy, or menopause can also affect the body’s hormonal balance and lead to flare-ups.

Medications

Sometimes, medicines can make chronic hives worse. NSAIDs, such as aspirin, ibuprofen, and naproxen, are common culprits. Prescription pain relievers, such as opioids, are another known trigger. Other medications, such as certain antibiotics (like penicillin) and blood pressure drugs called angiotensin-converting enzyme inhibitors, can have similar effects. Doctors note that acetaminophen is a safer over-the-counter pain relief option for people with chronic hives.

Talk to Your Doctor

Living with chronic hives can be challenging, especially when the cause isn’t clear. Keeping a simple hives diary can help you spot patterns. Write down when your hives appear, how long they last, and what you were doing before they started — like taking a hot shower or exercising. Even if there’s no clear pattern, share your notes with your doctor or allergist. They can help identify possible triggers, rule out other conditions, and discuss treatment options to keep the flare-ups under control.

Join the Conversation

On MyChronicHivesTeam, people share their experiences with chronic hives, get advice, and find support from others who understand.

What are your biggest triggers? Let others know in the comments below.