Yes, an allergy nasal spray, like Flonase, can help. You spray it on, let it dry, and then apply your sensor. It works very well if you have an allergy to the sensor/sensor adhesive patch.

Adhesives are also acidic, and a thin layer of Pepto Bismal applied to the skin can help if this is what you're reacting to. In this case, it is recommended that you use an alcohol wipe to clear a small area where the sensor will be inserted after applying the Pepto.

Cleaning a small area when using a skin barrier wipe is also recommended, as these can affect the sensor readings. Skin barrier wipes are another tool you can use for skin irritation. They, as the name suggests, form a barrier between the skin and the adhesive patch. Some are physical barriers, like a patch, with a hole cut out for the sensor to be inserted through, and some are wipes that are applied to the skin.

As you can see, there are several options for combating skin irritation. In answer to your original question though, yes, an allergy nasal spray can be used.