How long until Benadryl completely helps my dog's seasonal allergies?

You can monitor the area and see if there is any improvement. These spots look more like a bacterial skin infection than a pure allergic reaction so it wouldn't be surprising if there is no improvement. If this is an infection it could stay the same or get worse. If by tomorrow there is no response it is unlikely to be an allergy and Chevy needs to be seen by his veterinarian for treatment.

Given that the Benadryl didn't work to completely cure the allergic reaction, Giselle will likely need a steroid to stop it. I recommend having her seen by a vet now to get that prescribed to her to stop the reaction.

You should see an improvement of symptoms within a few hours of administration. If not, you can discuss a different antihistamine, OTC or prescription, with your veterinarian. Just as in people, different antihistamines may be more effective in different dogs. Allergies can be frustrating to diagnose, so discuss allergy testing, hydrolyzed diets and food elimination trials with your veterinarian in addition to antihistamine use.

Benadryl can be given to dogs to treat allergies but it is always best to check with your vet before giving medications. Since your vet knows your dogs complete medical history, he/she would know if there is a contraindication to giving any medications. Dogs with allergies can also develop secondary bacterial infection that may require an antibiotic, corticosteroid, and/or an anti-histamine to treat. If her signs persist or worsen then she should be seen by a vet to determine the best way to treat. There is also an allergy medication called Apoquel that works very well in controlling allergies in dogs. You could also switch to a completely hypoallergenic diet, like z/d, and see if that helps, too. Bathing her with a medicated dog shampoo, like Epi-Soothe, may also help.

Her behavior could be from the Benadryl but I doubt it as you gave an extremely low dose of it (I'm assuming you gave 1 tablet at 25mg - not 0.25mg). Benadryl is metabolized very quickly by dogs so they need a very high dose. The dose is 1mg per pound of body weight so she would have needed around 65 mg (so you would have to give 2 or 3 of the 25mg tablets for it to help much). You can refer to this information sheet about using Benadryl in dogs. ( https://www.petplace.com/article/drug-library/drug-library/library/diphenhydramine-benadryl-for-dogs-and-cats/ ) If you are worried about her behavior you should take her to the vet for an exam.

This is probably an allergic reaction due to an insect bite or a plant outside. those reactions tend to resolve within 48 hours without treatment. if the swelling becomes too large or if your dog becomes lethargic, take him to the vet in order to get an antihistamine/steroid injection. from your description at this moment i think he is probably fine, but this can change so monitor him closely.

If Chloe seems to be doing well I would suggest that you do discontinue the Benadryl. Dogs actually will build up a tolerance to the Benadryl if given consistently over a period of time. At that time it will either stop working or she will need more to get the same effect. You can always start it up again. The probiotic may help with allergies believe it or not so you can definitely do that - it will not hurt anything and might help. I like Fortiflora but you can use any probiotic made for dogs (not human ones or dairy). I do not have any first hand experience using this product but I have had a lot of people tell me it works well for allergies: http://www.dinovite.com/ You can also add the fish oil if you want to as well. It is always recommended. Hope this helps. Best wishes.