Answer

Aquagenic urticaria is a rare physical allergy that causes hives (urticaria) or itchy skin (pruritus) to develop rapidly after the skin comes into contact with water, regardless of its temperature. It’s considered a type of physical urticaria, where a physical stimulus triggers the reaction.

Symptoms:

• Hives: The primary symptom is the appearance of small, raised wheals (hives) that are typically 1-3 mm in diameter. These hives are usually surrounded by redness (erythema).
• Itching: Intense itching often accompanies the hives.
• Burning sensation: Some individuals may experience a burning or stinging sensation.
• Location: The reaction usually occurs on the chest, back, and arms, but can appear anywhere the skin has been exposed to water. The face is typically less affected.
• Onset: Symptoms typically appear within minutes of water exposure and resolve within 30-60 minutes after the skin is dried.
• Severity: Severity varies from person to person. Some experience mild itching, while others develop widespread and intensely uncomfortable hives.
• Other possible symptoms: Although less common, some individuals may experience:
  • Wheezing or difficulty breathing (rare, but possible if the reaction is severe).
  • Headache.
  • Fatigue.
  • Gastrointestinal symptoms (e.g., nausea, abdominal cramps) after drinking water, although this is extremely rare.

Causes:

The exact cause of aquagenic urticaria is not fully understood. It is not a true allergy to water itself. Water is a basic compound to the human body. Current theories suggest:

• Substance in the water: Some researchers propose that the reaction is triggered by a substance dissolved in the water, such as chlorine or other chemicals. This substance interacts with the skin to produce an irritant or allergen. However, individuals react to distilled water as well, making this less likely as a sole cause.
• Interaction with skin: The water may interact with an oil or other substance on the skin to form a toxic substance that triggers the release of histamine.
• Histamine release: Whatever the trigger, the underlying mechanism involves the release of histamine from mast cells in the skin. Histamine causes the blood vessels to dilate and become leaky, leading to the characteristic hives and itching.
• Genetic predisposition: There may be a genetic component, as some cases have been reported in families. It’s possible that certain individuals have a genetic predisposition that makes their skin more reactive to water.
• Autoimmune component: Some researchers suggest an autoimmune component, where the body’s immune system mistakenly attacks its own skin cells in response to water exposure.
• Abnormal keratinocyte function: Keratinocytes are the main cell type in the epidermis (outer layer of skin). Dysfunction in these cells might contribute to the development of aquagenic urticaria.

Diagnosis:

Diagnosis is usually based on a detailed medical history and a physical examination. A water challenge test is often performed:

• Water challenge test: A small amount of water (usually at room temperature) is applied to a small area of the skin (e.g., the upper back) using a compress for a specified time (e.g., 30 minutes). The skin is then observed for the development of hives or other symptoms. Distilled water is often used to rule out reactions to additives.

Differential Diagnosis:

It’s important to differentiate aquagenic urticaria from other conditions that can cause similar symptoms, such as:

• Aquagenic pruritus: This condition causes itching but without visible hives.
• Cholinergic urticaria: Triggered by an increase in body temperature, often due to exercise or sweating.
• Cold urticaria: Triggered by exposure to cold temperatures.
• Solar urticaria: Triggered by exposure to sunlight.
• Contact dermatitis: An inflammatory skin reaction caused by direct contact with an irritant or allergen.
• Other forms of physical urticaria: Urticaria triggered by pressure, vibration, or other physical stimuli.

Treatment:

There is no cure for aquagenic urticaria, so treatment focuses on managing symptoms.

• Antihistamines: These are the mainstay of treatment. H1 antihistamines, such as cetirizine, loratadine, or fexofenadine, are often used to block the effects of histamine and reduce itching and hives. Sometimes, higher-than-normal doses are required. H2 antihistamines, like ranitidine or famotidine, can be added to the regimen in some cases.
• Topical corticosteroids: These creams or ointments can help reduce inflammation and itching in localized areas.
• Barrier creams: Applying a barrier cream, such as petroleum jelly or a dimethicone-based cream, before water exposure can help protect the skin and reduce the severity of the reaction.
• UVB hardening: Some individuals have found relief with narrowband UVB phototherapy. This involves exposing the skin to ultraviolet B light in a controlled setting.
• Omalizumab: This is a monoclonal antibody that inhibits IgE, an antibody involved in allergic reactions. It has been used successfully in some cases of aquagenic urticaria when antihistamines are not effective.
• Epinephrine: In rare cases of severe reactions with breathing difficulties, an epinephrine auto-injector (EpiPen) may be necessary.
• Bathing strategies:
  • Limit water exposure: Take short, lukewarm showers or baths.
  • Avoid harsh soaps: Use gentle, fragrance-free cleansers.
  • Pat skin dry: Avoid rubbing the skin vigorously after bathing.
• Other medications: In some cases, other medications, such as leukotriene receptor antagonists (e.g., montelukast) or mast cell stabilizers (e.g., ketotifen), may be used.

Prognosis:

Aquagenic urticaria is a chronic condition, but the severity of symptoms can fluctuate over time. With proper management, most individuals can lead relatively normal lives. The condition doesn’t typically shorten lifespan, but it can significantly impact quality of life. The onset of aquagenic urticaria is usually in adolescence or early adulthood, but it can appear at any age.