Spit can feel like a sexy alternative to lube but use it in conjunction with lube. Spit will dry out quickly and you’ll need to keep adding more and more. Spit can, according to Cosmopolitan Magazine facilitate “the transmission of STIs and could introduce infection”.
Like baby oil, Vaseline or any petroleum-based jelly will wreck the condom you’re using (if you’re using one). If you’re not using a condom then you’ll find it a cheap alternative to other lubes on the market. You might find, because it is oil-based that operation ‘clean up’ afterwards is a little time consuming, especially if you get it on your sheets. There have also been studies that link petroleum jelly with the growth of yeast, which can cause problems – however, these studies have mainly focused on vaginal infections, so may not be an issue with PIA (penis is ass) sex.
Literally, don’t have penetrative sex without some sort of lube. You risk doing yourself quite a bit of damage. Without lube, you risk tears, bleeding and a really really uncomfortable screw. Also for someone without a foreskin, masturbation can be quite painful without some sort of lubricant. So it’s best to ask what your partner might be more comfortable with.