Antihistamines are medications commonly used to treat allergic reactions. They work by blocking the action of histamine, a substance released by the immune system during an allergic response. Antihistamines are effective in relieving symptoms such as sneezing, runny nose, itching, and watery eyes that are commonly associated with nasal allergies.

However, antihistamines are not helpful in curing nasal allergies completely. Nasal allergies, also known as allergic rhinitis, are chronic conditions that are typically caused by an overactive immune response to allergens such as pollen, dust mites, pet dander, or mold spores. While antihistamines can provide temporary relief from symptoms, they do not address the underlying cause of the allergy or provide a long-term cure.

While antihistamines are not helpful in curing nasal allergies, they are effective in treating rashes caused by itching. When histamine is released in response to an allergen, it can cause itching and lead to the development of rashes. Antihistamines can help reduce the itching sensation and provide relief from the rash.

Similarly, antihistamines are also not helpful in bringing down acute fever. Fever is typically caused by an infection or inflammation in the body. Antihistamines do not have direct antipyretic (fever-reducing) properties and are not effective in lowering body temperature. Medications such as acetaminophen or ibuprofen are commonly used to reduce fever.

On the other hand, antihistamines can cause vasodilation, which is the widening of blood vessels. This can lead to a decrease in blood pressure and increased blood flow to certain areas of the body. However, the statement in the question is incorrect as antihistamines are not used for vasodilation purposes. There are other medications specifically designed for vasodilation, such as nitrates, which are used to treat conditions like angina or heart failure.

In summary, antihistamines are not helpful in curing nasal allergies or bringing down acute fever. They are effective in treating itching and associated rashes, but they are not used for the purpose of vasodilation.