Causes and Risk Factors of Hives

Hives—also known as urticaria—is an inflammatory skin disorder that causes itchiness and red or skin-colored bumps on the body called wheals. Cases of urticaria can also have larger patches of swelling (angioedema). Having hives is a sign that your immune system and skin are reacting to a sensitivity, allergen, irritant, or infection. 

Most chronic hives—which last more than six months—are idiopathic, meaning they have no known cause. Other cases of hives occur due to known factors. For example, acute urticaria, which may resolve on its own within six weeks, can be triggered by allergens, exposure to insect venom, medication side effects, and certain infections. Some cases of hives can be inducible, meaning they are triggered by environmental factors, such as heat, cold, water, or sweating, among others.

Infections

Among the most common causes of hives are viral, bacterial, or parasitic infections. This is particularly the case in children and infants, accounting for up to 80% of acute outbreaks in this population. Infections can trigger your immune system into action, leading to urticaria flares—though more research is needed to understand how.

The most common viruses noted to cause hives include: 

• Rhinovirus: Causes the common cold
• Rotavirus: Causes the stomach flu
• Epstein-Barr virus (EBV): Can cause mononucleosis (commonly known as "mono")
• Hepatitis A, B, or C viruses (HAV, HBV, or HCV): Infections that affect the liver
• Herpes simplex virus (HSV), known as herpes: A common viral infection that can cause sores on the mouth, lips, and/or genitals
• Human immunodeficiency virus (HIV): A virus affecting the immune system that can lead to acquired immunodeficiency syndrome or AIDS

Hives may also arise due to bacterial infections. Cases have been linked to:

• Urinary tract infections (UTIs): An infection in any part of the urinary system which can result from different types of bacteria
• Streptococcus: A group of bacteria that cause strep throat and skin infections called cellulitis
• Mycoplasma: A group of bacteria that cause respiratory infections
• Helicobacter pylori: A type of bacteria that causes stomach infection

Chronic urticaria has also been linked to different diseases caused by parasites—microscopic organisms that survive off other organisms. A parasite can enter your body when you drink contaminated water, come into contact with fecal matter, or through other environments. Often affecting your stomach and intestines, some parasitic infections which can trigger hives include:

• Giardiasis: Caused by Giardia parasites, often found in water
• Ascariasis: Caused by Ascaris parasites, often found in soil or feces
• Anisakiasis: Caused by Anisakid parasites, often found in raw fish or squid
• Toxocariasis: Caused by Toxocara parasites, commonly found in dogs or cats

Allergens

Urticaria can occur during an allergic reaction. These arise when your immune system misreads an allergen—a usually harmless substance—as an invader, then attacks the allergen using an antibody (a blood protein) called immunoglobulin E (IgE). This type of allergic reaction is called an IgE-mediated response and often happens almost immediately after being exposed to the allergen. 

Allergens that may trigger this IgE response and lead to hives include:

• Certain foods, such as eggs, milk, peanuts, soy, and wheat
• Some antibiotics, including penicillin and cephalosporins
• Latex, such as some gloves, balloons, and condoms
• Physical contact with certain plants, raw fruits, and vegetables
• Bites or stings from bed bugs, bees, wasps, hornets, and fire ants 
• Pollen, mold, or dust mites    

Nonsteroidal Anti-Inflammatory Drugs

Nonsteroidal anti-inflammatory drugs (NSAIDs) are common medications used to reduce pain and inflammation. Some types include Advil (ibuprofen), Bayer (aspirin), and Aleve (naproxen).

Some people who take NSAIDs may have allergic reactions (IgE-mediated). Other people may have pharmacologic reactions; these are pseudo-allergic reactions that don’t involve IgE antibodies but still cause inflammation.

In either case—whether allergic or pseudo-allergic, you can develop hives within minutes of taking NSAIDs. Though, some pharmacologic reactions can lead to hives one to two hours after.   

Direct Effects of Drugs 

Certain medications and plant chemicals can trigger inflammatory skin reactions in some people. Your immune system reacts using mast cells—a type of white blood cell found in your skin cells and other parts of your body. This type of allergic reaction is known as direct mast cell activation (it is not IgE-mediated). 

Hives, swelling, and other allergic symptoms can develop anywhere from a few minutes to hours after being exposed to the drug or substance. The timing can vary depending on whether you take the drug as a pill or intravenously (via IV), or if the contact was through touch. This is the case with:

• Opiate drugs, such as morphine, codeine, and dextromethorphan (an opiate derivative found in some cough syrups)
• Muscle relaxers like Tacrium (atracurium), Norcuron (vecuronium), and others
• Vancomycin, an antibiotic
• Stinging nettle, a plant that’s also called Urtica dioica

Environmental Triggers

Some people can develop hives when their skin is exposed to certain environmental or physical factors. These types of hives are called inducible urticarias or physical urticaria.  These hypersensitive conditions can occur in 20% to 30% of adults with chronic hives (about 1% of adults have chronic hives).

In most cases, people with inducible urticaria have an underlying condition that makes their skin hypersensitive to a certain trigger. Some triggers and their conditions include:

• Heat: Heat urticaria
• Cold: Cold urticaria
• Water: Aquagenic urticaria
• Sweat: Cholinergic urticaria
• Pressure on the skin: Delayed-pressure urticaria or angioedema
• Vibration: Vibratory angioedema and urticaria
• Direct sunlight or UV light: Solar urticaria, polymorphic light eruption (PMLE), and other photodermatoses (photosensitive conditions)
  

Is Hives Genetic?

Researchers have found that some types of hives can happen in people with a genetic predisposition. This is supported by studies about identical twins and their shared urticaria (compared with fraternal twins, who don’t have identical DNA). Other studies suggest that certain gene variants (genetic polymorphisms) can increase someone’s susceptibility to acute urticaria that’s triggered by NSAIDs.

There may be a hereditary factor as well; about 25% of people with chronic spontaneous urticaria had a family history of the same condition.

Not only that, a rare form of cold urticaria is hereditary and is caused by an autosomal dominant mutation on a chromosome. This means if you have a parent who carries at least one copy of the mutation, you will have a 50% chance of developing this condition. 

Who Gets Hives?

Aside from genetics and hereditary factors, some people are more likely to develop hives than others. This can vary by:

• Age: Children aged 5 and under experience acute urticaria at a higher rate than those older. Adults over 30 are more likely to experience chronic cases.
• Sex: Women are more likely to experience chronic hives, and those over age 30 have the highest rate of chronic spontaneous urticaria (which has no known cause).   
• Ethnicity or race: While all ethnicities can develop hives, a few studies have found that Black and Latino people may experience urticaria at a higher rate than white people, though socioeconomic differences and environmental factors may play a role.  

Risk Factors

Certain diseases and conditions increase the risk of developing acute and chronic forms of hives. Not only that, geography and economic status can also increase the chances of developing urticaria. 

Geography

Where you live can serve as a risk factor. In particular, living in areas with higher population density may raise the risk of developing urticaria.  Living at a higher altitude and in an area with higher temperatures may also increase the chances of urticaria.

Economic Status

Poverty and lower socioeconomic status increase the risk of developing acute urticaria. However, for chronic cases, higher socioeconomic status serves as a risk factor.

Other Conditions

Living with or having a history of certain health conditions may increase the chances of developing hives. For example, studies show that women with peptic ulcer disease (a condition characterized by acid in the digestive tract that damages the inside of the stomach or small intestine) or abnormal uterine bleeding (irregular or extending bleeding in the uterus) may have an increased risk for chronic urticaria.

Conditions Linked to Chronic Spontaneous Urticaria 

Representing a majority of chronic urticaria, spontaneous urticaria or idiopathic urticaria is a type of hives with no identifiable trigger. Some spontaneous hives may be associated with other conditions—though more research is needed. These conditions include: 

• Allergic diseases: In a study of over one million 16-year-olds, those with chronic spontaneous urticaria found they were more likely to have allergic diseases, such as food allergy, allergic rhinitis, atopic dermatitis, and asthma.
• Autoimmune disorders: Several studies have drawn links between spontaneous hives and autoimmune diseases, in which the immune system is hyperactive and mistakenly attacks the body. These autoimmune conditions include celiac disease, Sjögren’s syndrome, systemic lupus erythematosus, rheumatoid arthritis, and type 1 diabetes.   
• Thyroid disorders: Of the autoimmune conditions linked to spontaneous urticaria, thyroid disorders may be the most common. In a study of over 12,700 adults with spontaneous urticaria, about 9% had hypothyroidism (underactive thyroid) and over 2% had hyperthyroidism (overactive thyroid).

A Quick Review

Urticaria is an inflammatory skin disorder that causes itchy hives to form on the body, along with swelling (angioedema) in some cases. This condition can happen in some people due to exposure to allergens, infections, and taking certain medications.

While all can be impacted, children are more likely to develop acute urticaria, and urticaria tends to be more common in women than men. You may have a greater risk of developing hives if you have certain health conditions or lower socioeconomic status and live in densely populated areas.