Note: I plan to update this post when I can with some examples of yellowing from my personal collection.
You can't reverse yellowing. The good news is that yellowing is very, very gradual. You're not going to see severe yellowing in your doll just from walking to your car and back. They may mellow within a year or so, but you will not see severe yellowing for the most part until after many years of love and play.
Most people find they barely notice the yellowing, because it is something that happens so slowly you often don't notice until you compare the inside of a doll's headcap or a newer doll from the same company to an older one.
Is Yellowing Damage?
In most cases, yellowing should not constitute damage. What yellowing can indicate in a newer doll is a lack of care and preservation for the doll itself. Blotchy yellowing, or the yellowing equivalent of a farmer's tan could be considered damage in most cases. You're obligated as an honest seller to disclose any yellowing. Personally, any doll at least a year or more I always note that it probably has some yellowing.
