It's the Callington Haven Knockdown spray. Here is the manufacturers PDF:
http://www.callingtonhaven.com/_assets/knockdown.pdf
The aircraft is supposed to be sprayed no more than 1 hour prior to pushback, so is generally done immediately before boarding of passengers begins with 3 cans of 100ml each. (Aircon packs are switched off, one door open only during the spray as well).
I've never had anybody have any kind of reaction to the spray, beyond the look of horror on the crew's face as they frantically try and cover the cup of coffee they are holding as the spray comes down the cabin.
On board allergy medications include antihistamines, epinephrine, (including epipen auto-injectors) promethanzine and dexamethasone.
Hope that helps.