Your baby's tender skin has been kept completely sterile for 9 months inside your belly. Once your baby arrives, your baby's skin is exposed to cold, dry air, perfumes, dirt, and soap. Your baby's skin is especially sensitive and all soaps, even baby soaps, are mild irritants.
Your baby's skin will react differently to different baby soaps. Which baby soap to use, how much, and how often can only be determined by trying different soaps and starting small and watching how your baby's skin reacts over time.
All baby soap is made from the same soap adults use with fewer anti-microbial, fragrance, and abrasive additives. Some baby soaps are made of natural plant oils, natural essential oils, milk proteins, vitamin E, and other moisturizers such as aloe vera or oatmeal.
Most baby soaps are commercially made, but a wide variety of handmade soap or natural baby toiletries are available. Always choose a mild baby soap specifically formulated for babies. Baby soap should be as gentle as water on your baby's skin.
When first using baby soap, try a patch test on one small part of the body, usually under the arm or the wrist. If the skin reddens, dries, or noticeably changes in any way within 24 hours, try a different brand of soap.
Limit the amount of time soap is on your baby's skin. Try to keep soap on your baby's skin for no more than five minutes to avoid drying or irritation. Lather your wash cloth with soap, gently wash your baby, and rinse your baby well.
Newborns really only need a thorough rinse with warm water; older babies will need something with a little more substance on their dirtiest parts. Use baby soap only on areas that are caked with dirt, oil, or sweat which can not be easily removed with warm water. Soap is useful for those areas of caked on and sticky goodness, but the goal is to minimize the amount of contact soap has with your baby's skin.
If your baby develops eczema or skin allergies, use as little baby soap as possible, and give as few baths as possible. A special soap prescribed by your doctor may be helpful.