Personal lubricants colloquially termed lube are specialized lubricants used during human sexual acts such as intercourse and masturbation to reduce friction to or between the penis and vagina , anus or other body parts or applied to sex toys to reduce friction or to ease penetration. Surgical or medical lubricants or gels, which are similar to personal lubricants but not usually referred to or labelled as "personal" lubricants, may be used for medical purposes such as speculum insertion or introduction of a catheter. The primary difference between personal and surgical lubricants is that surgical lubricants are thicker, sterile gels, typically containing a bacteriostatic agent. Water-based personal lubricants are water- soluble and are the most widely used personal lubricants. The earliest water-based lubricants were cellulose ether or glycerin solutions. Products available today may have various agents added for even dispersal, moisture retention, and resistance to contamination.