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Atypical Acquired cold urticaria (ACU) is a type of physical urticaria caused
by the release of  mast cell mediators which lead to inflammation following exposure to cold. The underlying causes of ACU remain to be clarified in detail, a wide range of
diseases are associated with ACU.

Research Gate Report – PDF format
Me and My Mastcells
Familial Atypical Cold Urticaria: Description of a New Hereditary Disease

Systemic cold urticaria (generalized urticaria occurring upon exposure to cold) was first reported in 1984. This form of Atypical Cold Urticaria is characterized by reactions that occur on multiple areas of the body, not just the area exposed to the cold (localized).  Symptoms are difficult to control and the Cold Stimulation Timed Test (CSTT) (aka; Ice Cube Test) is always negative.

What sets this condition apart from Reflex Cold Urticaria is that reactions do occur at site exposure as well as other areas. RCU reactions do not occur at site of exposure, but other areas of the body.

Cold Induced Urticaria
Cholinergic Urticaria (ChU) is commonly triggered by heat, exercise and/or sweat.  A more rare form is triggered by cold.  The difference between this condition and Cold Urticaria is that Cold Induced has an appearance where the wheals are very small, pinpoint size.  They are intensely itchy.  The CSTT test will be negative.

The mechanism by which the cold stimulus is transformed into a signal for molecular and cellular activation has not been elucidated. Anti-IgE antibodies may play a role.

Identification of a new physically induced urticaria: cold-induced cholinergic urticaria
Cold-Induced Cholinergic Urticaria – A Case Report
A Case of Combined Cholinergic and Cold Urticaria
Evaluation of a patient with Cold and Cholinergic Urticaria

Reflex CU

Reflex CU presents with small weals in the vicinity but not at the place of contact with cold. The lesions occurred only on the extremities and during the cold season.
Localized Cold Reflex Urticaria.

Cold Dependent Dermographism/Dermatographism
Dermatographism that is observable only upon chilling the skin subsequent to scratching it. The reaction can be associated with detectable elevation of venous histamine levels coincident with the development of urticaria.

An alternative presentation involves generalized urticaria that is induced by systemic rather than local cold challenge. The reaction can be anaphylactoid in nature and associated with systemic elevation of histamine levels.

Unusual cold-induced disorders: cold-dependent dermatographism and systemic cold urticaria

Delayed Cold Induced Urticaria
Delayed cold urticaria may appear several hours after contact with the cold.

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Nuggets of Wisdom

Yes, there is such a thing as having an allergic type reaction to temperatures. This is defined as a physical urticaria. Other physical urticarias include Solar, Aquagenic, Pressure, Vibration and Exercise.

Most reactions are pseudo-allergic. By definition, an allergy involves inhaling or consuming an allergen. Physical urticarias have no known allergen. Despite the terminology and medical definitions, systemic reactions can be life threatening.

Cold has an arbitrary definition based on an individual feeling. For a person with a cold urticaria, cold can be defined as any temperature cooler than their own body temperature.

You do not have to be cold to have a reaction to the cold; contact with cold can trigger a reaction.

You can have an allergic type reaction to both cold and heat simultaneously.

Most reactions considered anaphylactic are really anaphylactoid by definition.

Moving to a warmer climate as a treatment for Cold Urticaria is a myth. Warmer climates present their own issues for those with Cold Urticaria.

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