How do pastes differ from ointments and creams?

Ointments are petroleum based - thus the slightly greasy feeling. Creams are water based. As for which is appropriate for usage - I go by this rule. Creams tend to dry out the area on which they are used (which are great for things like acne, etc). Ointments will hydrate the skin more - so if the skin is dry to begin with (not oily), then ointment is your best bet. You should be able to get both the ointment and cream in the same strength (% solution). Hope this helps.