I used regular detergent, just did an extra rinse cycle. Never had an issue. Some babies have more sensitive skin than others.
It all depends on your baby. If they have sensative skin, than you will want to use a detergent that's is free and clear of all dyes, nut don't necessarily need to pay the extra for "baby" detergent. So e babies are ok using whatever your used to.
FIRST OF ALL MAKE SURE THAT YOUR BABY IS NOT ALLERGY IN ANY DETERGENT SOAP. BABY'S SKIN ARE SENSITIVE. YOU CAN ALSO ASK YOUR BABY'S DOCTOR TO.