What are the symptoms of a tattoo-related infection (photo)?

It does sound like your son may have hives or urticaria and has been prescribed with telfast. Telfast is a second generation antihistamine which is a non-drowsy antihistamine as it does not cross the blood brain barrier. While there are not many studies on the long term use of the antihistamines, it is generally believed that the 2nd generation antihistamines are safe for use in the long term. We must always weigh the risks vs benefits of taking the medicines for the long term, but the risks with long term antihistamines is low.

Thank you for the question. The photo of the rash can go for eczema. The rash in eczema is usually itchy, and aggravated by scratching. Persistent scratching or reaction to certain creams applied can cause the rash to be recurrent or persistent, so your mother should refrain from scratching as far as possible. If the rash is still persistent despite treatment, you may want to consider seeing your doctor/dermatologist to rule out an underlying cause for the persistence, such as a fungal infection or allergic contact dermatitis.