Can i put cologne on my 4month old baby? what is safe?

No: It doesn't sound like a good idea. Babies smell just fine. If a baby smells badly, the parents can talk to the pediatrician about it. It's probably not harmful to put very tiny amounts of cologne on a baby's skin, but it shouldn't be needed. A baby is just fine without any perfume chemicals.

Please don't: Please avoid placing any fragrance or smell on or near baby. It irritates their nasal passages and can lead to nasal congestion/cough and a higher risk of respiratory infections. Adults have a large nasal chamber (compared to baby) and nasal membranes more tolerant to smells. Just because you like the smell and it doesn't bother you does not mean it is good for baby.