Aquagenic urticaria, also known as water allergy, is considered the rarest allergy. It is a condition that causes itchy and painful hives to break out whenever the sufferer comes into contact with water. These hives occur as a result of the body’s mast cells releasing histamine, which creates the hives. Changing the water temperature has no impact on the allergic reaction, and there is no effective treatment, although anti-pruritic lotions or creams can help to soothe the itching. Other rare allergies include:

• Exercise allergy (solar urticaria): Symptoms include an outbreak of hives when exposed to the sun. Anti-histamines and sunscreen can help to keep reactions to a minimum, and although there is no permanent cure, in some rare cases, the condition can go away on its own.

• Money allergy: The culprit is the compound called nickel sulfate in loose coins. Doctors recommend avoiding contact with coins and using credit cards instead.

• Cold allergy (cold urticaria): While most cases of this rare allergy come from a genetic gene mutation, there are several cases of people who have the allergy without the mutation. For them, professionals are unsure as to what causes them to develop the allergy. Symptoms include hives, swelling, and even anaphylaxis.

• Sunlight allergy (photosensitivity): This condition causes individuals to develop hives on their skin when exposed to sunlight. Anti-histamines and sunscreen can help to keep reactions to a minimum, and although there is no permanent cure, in some rare cases, the condition can go away on its own.

It is important to note that while these allergies are rare, they can still occur, and people who suffer from them should take precautions to avoid exposure to the allergen.