Hello, what s more important is that this behavior is inevitable. It s in the nature of children to taste things. Infants feel the world with their mouths! Tasting surfaces that other hands have touched, exposes the baby to risk for infections (respiratory mostly). Germs seem to be good for babies because they lessen the risk for allergies etc. I don t believe there is a definite answer for your question but my personal opinion is that infants should come into contact with the environment and allow them to taste toys etc that have fallen into the ground but there are some limits that should not be exceeded. I wouldn t advice giving to the baby a toy that has visible dirt on it or touching something that a diseased person has touched. There is no need for a diarrheal disease or for a respiratory tract infection. Please also note that the most commonly acquired infections are mild and self-limiting but you can t exclude serious life-threatening infection like tuberculosis for example. So letting the kid explore its surroundings is nice but parents should protect it against serious conditions that can t be predicted... I hope I ve helped! If you d like more information please let me know and I ll be glad to answer. Kind Regards!