When babies are first born their skin can often be quite sensitive and it is more likely that they will experience irritation from washing powders and different materials. Cotton is said to be one of the best materials for your baby to wear as it is soft and ensures that the skin is kept dry.
When washing any clothes for a baby, you should always opt for a non bio type. This means it is non biological which ensures it is gentler on the skin. Non bio is often said not to get as many of the stains out as biological powder but it is definitely the safer option at this stage.
If your child starts to come out in a rash or seems to be unsettled it may be that the type or washing powder you have used or the material that they are wearing, is causing them discomfort. If this is the case, then it is best to seek professional help to find out if there is any treatment they may need to have or if you just need to allow it to clear on its own. It may be that they need antihistamine or even steroids for extreme cases.