I never used anything but regular laundry detergent to wash my son's clothes, but I always made sure everything of his was washed before he ever put it on.

With my first born, I did everything by the book. Bought Dreft, yada, yada yada. Then I started using All Free & Clear. I was told by our pediatrician that Tide leaves a residue on the clothes that can cause irritation, which my son got when he was first potty training and was wearing underwear.

I have liked All (Free & Clear) which I still use today. I always let their clothes air dry that way they are less likely to shrink and will last longer. It's really just up to you. I always used cold water on everything but the underwear and that gets washed on HOT water.

I would like to add to the answers that we use no special detergent, but when washing stuff for our son we use a special setting on our machine which rinses twice to get all of the detergent out of the cloth. We also try to avoid perfumed detergent and don't use fabric softener.

We used All Free Clear for the first several months then started putting the baby clothes in with the rest of the laundry. When we were in the store deciding which detergent to get we compared Free Clear to All Baby and Dreft. The only difference in the ingredients was that the ones marketed for babies had a perfume in them. The Free Clear was less money for a larger bottle and perfume free.

According to these studies on the Proctor and Gamble website (they may have a vested interest) biological detergent is not more likely to cause irritation than non-biological. In general I think there's no harm in making sure that everything gets rinsed thoroughly after washing. If you are wary about using fabric softener you can put white vinegar in the rinse drawer and that helps to get any detergent residues out and so softens clothes.

From a personal experience point of view - I wash most of our clothes and our son's nappies in non-biological. Only using biological on my husband's shirts, which seem to get very smelly otherwise. On the unfortunate occasion when I had forgotten to take detergent with us on a visit to relatives, and our son's nappies got washed in biological detergent, his foreskin became rather red and inflamed. The inflamation went away once I had rewashed all the nappies in our usual, non-biological, detergent. That's quite an extreme case though - the most sensitive part of his anatomy in wet contact with possible detergent residues for several hours.

I use Dreft because it's what my mom always used. She defended the cost by explaining that it's better for baby skin and it's better with getting out certain biological stains. (Apparently my grandma starting using Dreft again when she was having trouble maintaining her bowel movements.) However, I'm having trouble getting it to just take out those stains. I'm going to try soaking the soiled onesies in warm water and Dreft. I'll post back later on with the results.

Results: Soaking worked for one of the four garments, but it was the one I'd scrubbed immediately after it happened.

We also washed everything, new things were washed with the short cycle with mild detergents and fabric conditioners to begin with. Once it was more evident that she didn't have very sensitive skin we used our normal detergents and fabric conditioners. For articles of clothing given to us, these were washed at 50 degrees on a longer wash cycle and then rinsed with fabric conditioner as well.

I cannot say whether using milder detergents would be better or not, but I would definately recommend starting with the milder detergents first. Best of luck!