I use hand lotion daily to keep my hands from getting overly dry and cracking. Can I do the same on shabbos when my hands start feeling dry? If not, can I use lotion before I feel I need it, as a preventative measure?
The question of a wise man is half the answer. nevertheless here is a brief introduction. Medication and the like are prohibited on shabbos. (with exceptions of course for Doctor prescribed medications-beyond the scope of this post). As a result any lotion applied for a medicinal purpose such as dry hands would be prohibited. On the other hand (no pun intended) to luxuriate ones hands with lotion in a non medicinal application is permitted. Therefore the answer to your question really depends. If the status of your hands at present are soft and supple there would be no problem of using the lotion, even if it will prevent it from cracking in the future. But if your hands already feel dry and your intention is to relieve the discomfort it would be considered medicinal,
can lotion be used on a baby’s skin that is very dry even though it is for medicinal purposes?
is ointment or a thicker cream ok?
A baby is different in regards to the above and it would be permissible to smear the skin. Additionally the only prohibition to smearing on shabbos would be an action similar to spackling a wall meaning your intention is to make a nice smooth layer of ointment, but if it is done in a haphazard way without intention to make a nice layer there is no issue with smearing.