Vicks Vapor rub for 4 mo old

My son has a terrible cold and cough (no fever), so I set up his cool most humidifier and I put a little vapor rub on the back of his neck to help him breath better. We went to the doctors today and it's nothing but a snotty baby cold, but I never asked if the vapor rub was safe for a 4 month old? I just assumed. It's not actually "Vick's", it's an organic menthol rub, but I just call it Vicks. Anyone else use it on their babies before? Should I worry? I just worry more about his cold. I also have the stuff you can put in the humidifier, too. That one actually is the brand Vick's, but I didn't wanna wake him messing with his humidifier so I just rubbed a little of the rub kind on him instead.