Pet and dog dander and other pet or dog allergens can stay in the house for as long as 1 month to 6 months after you get rid of the dog.
If you or someone is allergic to a dog then you will likely have to get rid of the dog to prevent allergy flare ups or at least have the dog outside if it's warm enough.
No matter how much you love the dog sometimes you have to give up the dog to protect you or your families health.
Dog dander can be in the form of hair and skin particles that you can barely see especially if the dog scratches their body and sends fur and skin flakes that are microscopic through the air.
Make sure the dog doesn't get near your bedding if you're allergic to them and wash them often and groom them often to keep dog hair from shedding all over the place.
Make sure to vacuum the carpets often as well to remove pet dander and pet hair from the carpet and upholstery if your dog gets on the upholstery.