Both Vaseline and baby oil will degrade the neoprene, and act as a solvent on the glue, so should be avoided. Some sun creams also cause problems (making the neoprene go sticky) If you want extra lube on the knees and neck use silicone grease or nappy cream (although I have never felt the need with a cell interior)
If you are sensitive to hair conditioner, Subskin is very good
www.subskin.it but is is a more expensive option
cheers
dave
www.spearo.co.uk