What the itch?

Contact vs environmental allergy

You might hear these terms bandied about, and to be honest it can be difficult to differentiate between them, especially if the itch is only intermittent.

Contact allergy occurs in sensitised animals when they come directly in contact with the offending substance. The classic example in New Zealand is dogs running through the plant Wandering Jew. Other known contact allergens are the broadleaf grasses Paspalam and Kikuyu, and Agapanthus has been suspected as well. The plant directly irritates the skin and causes a rash where it touches – most usually the paws, inside the legs and under the tummy. Cats are less prone to contact allergies as their denser fur protects them.

Environmental allergies are caused by substances such as pollens, mould spores, and dust mites. They are absorbed across a faulty skin barrier and trigger the immune system to produce a more generalised reaction. Redness and itchiness often occur in the armpits, groin, feet and ears – so not dissimilar to the reaction pattern for contact allergy. Most environmental allergies initially start as a seasonal itch, but over time as the animal becomes allergic to more things, it can become a year-round problem.

How to tell them apart? The first clue might be that the itchiness seems worse after a walk to the river, or there are long periods with no itch, and completely normal skin in between episodes.

If there is a high suspicion for contact allergy, patch tests can be undertaken with the usual culprits to see if there is any reaction. Alternatively, avoiding areas where the suspect plants grow for two to three weeks should result in an improvement and confirm the cause. Once confirmed the best method for management is avoidance, or bathing as soon as possible after contact to remove residue from the skin.

Environmental allergies however require lifelong management – too much information to go into detail here! If you have any concerns about your pet’s skin, try and keep a diary of when things seem to be worse – it might give a clue to the answer!


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