After wudu

Ablution is necessary after relieving yourself (including passing of gas) or sexual discharge, as evidenced in the Qur'an (5:6) which says:

...one of you comes from the place of relieving himself or you have contacted women...

From the sunnah, ablution is to be performed anew after deep sleep. Most (but not all) scholars also consider ablution invalidated by merely touching the private parts (even if there is no discharge).

Creams and petroleum jellies and other such products applied to the body do not fall under any of the above categories, and I know of no evidences to suggest that they would be treated with any especial importance. The only concern for applying these would be that if you need to perform the ablution later, the product should not be such that it blocks water; many scholars only consider the ablution valid if water reaches the skin.