I nanny for infant twins who had terrible cradle cap. We began using a cotton ball to apply undiluted organic apple cider vinegar to their heads twice on bath day only, which is twice a week for them. To my knowledge, this was just to control the smell. Within a week or so, the cradle cap had drastically improved and after 2 weeks, was completely gone. We continue the application to ensure that it doesn't come back. I'm a believer and now am looking into remedies for myself!
My Chiropractor told me to use vinegar on my baby girl's cradle cap. I applied it straight and let it sit for 10 minutes before her bath. I've done this only four times now and her cradle cap is almost gone already!!! Maybe this straight vinegar treatment could work for other scalp problems as well.