Answer:
firstly it depends
Step-by-step explanation:
Purple shampoo contains high levels of citric acid, an ingredient in lemon juice, which plays a role in lightening the hair. While citric acid is safe to consume for humans, high levels are not suitable for dogs, causing irritation, upset stomach and can even be toxic. purple shampoo if in a small amount then it's fine but in large quesntity it needs to be checked . it's also based on the sulphate content.
hope it helps