Hi GardenPrincesses!
to All Things Plants from me too!
I grow a couple of Hoyas and they do have that white milky sap which can cause contact dermatitis in some humans. I've always had hundreds of houseplants and I've had many pets over the years; cats, dogs and birds. We had a cat once who liked to get into the plants, mostly eating African Violet flowers and we currently have one dog and are trying to train him to not munch on any plants because so many can be toxic to animals. I don't know that the flowers of Hoya would be harmful but I'd be concerned about children or pets eating the stems or leaves with that milky sap.
@AlohaHoya may be able to offer advice on the possible toxicity levels of Hoya plants.
