What is aquagenic urticaria?
Aquagenic urticaria is a rare variant of chronic inducible urticaria induced by contact with water [1,2].
Who gets aquagenic urticaria?
Less than 100 cases of aquagenic urticaria have been reported in the medical literature . There is a higher prevalence among females, with the typical age of onset during or after puberty . Most cases have occurred sporadically, but several familial cases have also been reported .
What causes aquagenic urticaria?
The exact pathogenesis of aquagenic urticaria is not yet known, but a number of hypotheses have been proposed.
Water reacts with unknown components within the skin, causing histamine release from mast cells and the formation of an urticarial rash. Triggers may include:
- Still or running fresh water
- Sweat and tears .
Aquagenic urticaria appears whatever the water temperature, saltiness, or pH, and is not dependent on psychogenic factors .
What are the clinical features of aquagenic urticaria?
Skin contact with water results in symptoms within 20–30 minutes.
- 1–3 mm folliculocentric weals surrounded by 1–3 cm erythematous flares resembling cholinergic urticaria .
- The rash mainly affects the trunk and upper arms, with palms and soles typically spared [1,2,5].
- The rash may spread to involve areas that are not in contact with water.
- The weals normally resolve spontaneously within 30–120 minutes after cessation of contact with water .
- Associated symptoms may include pruritus, burning, and prickling .
Rarely, the patient may also experience systemic symptoms of wheezing and shortness of breath .
What are the complications of aquagenic urticaria?
Intense or prolonged itching results in excoriations that can be secondarily infected and start to ulcerate and scar.
Patients with aquagenic urticaria may suffer from psychological stress due to a fear of water.
How is aquagenic urticaria diagnosed?
A clinical history of urticaria in response to water exposure is suspicious of aquagenic urticaria, but the diagnosis should be confirmed by a positive water provocation test and exclusion of other types of chronic inducible urticaria.
Water provocation test
A water provocation test can be performed to test for aquagenic urticaria using the following method:
- Apply water at room or skin temperature to a cloth
- Apply the wet cloth to the patient’s upper trunk skin for 30 minutes
- Assess skin for an urticarial reaction [1–3,5].
To exclude cholinergic urticaria, examine for urticaria after an exercise test to raise the core body temperature . Other physical urticarias to exclude on testing include pressure urticaria, cold urticaria, and heat urticaria.
What is the differential diagnosis for aquagenic urticaria?
Aquagenic urticaria must be distinguished from other forms of inducible urticaria, including :
- Salt-dependent aquagenic urticaria — seawater provokes lesions but not freshwater
- Aquagenic pruritus — water exposure causes itch with no associated skin lesions
- Dermographism — common physical urticaria with linear weals
- Cholinergic urticaria — weals are morphologically similar to those of aquagenic urticaria but appear with an increase in core body temperature rather than exposure to water
- Cold urticaria — cold contact produces pruritic weals
- Delayed pressure urticaria — pruritus, swelling, and pain 4–8 hours after the skin is exposed to pressure
- Exercise-induced anaphylaxis
- Local heat urticaria — limited to the area of heat exposure
- Solar urticaria — an immediate reaction to ultraviolet radiation that resolves within 24 hours
- Vibratory angioedema — erythema and angioedema beyond the provocation site.
What is the treatment for aquagenic urticaria?
As it is impossible to avoid water completely, treatment is aimed at preventing or minimising symptoms induced by contact with water.
The main treatment is to take a daily non-sedating, second-generation H1 antihistamine, such as cetirizine, loratadine, or fexofenadine prophylactically .
Other reported treatments include:
- First-generation H1 antihistamines
- H2 antihistamines
- Acetylcholine antagonists, such as scopolamine
- Omalizumab 
- Petrolatum-coating .
What is the outcome for aquagenic urticaria?
The rate of remission of aquagenic urticaria is unknown.