It is still potent in the winter. Even when it loses it's leaves it can cause a reaction. It's the oils of the plant that cause the reaction. So if you come in contact with it wash as soon as possible with a soap that breaks up oils. I found most dishwashing soap work very well. It's easier to deal with in the winter because of the lack of leaves. As for pets I don't know for sure but my dogs and cats don't seem to have a reaction from it. However if it gets on their fur it can than be spread to you.