Any solution - oil or water based that helps increase motion and cut down on friction can be considered a lubricant - even just plain water.
Everybody at some time is going to need a lubricant and for some sexual activities it an absolute MUST.  For women, there are times that the body just does not generate enough vaginal fluid and many things can affect this - time of the month, stress, recent child birth, antihistamines, decongestants, menopause, antidepressants, antihypertensives and cardiac agents. All of these things can contribute to vaginal dryness. Under any of these circumstances a lubricant will make vaginal penetration more pleasurable. In this age of safer sex the use of a lubricant on the inside of a condom can make the sensations delivered to the penis much stronger.  Anyone that is using some adult sexual aid should consider a lubricant because of the dryness of the materials that adult toys are made from. For anyone engaging in any kind of anal sex a lubricant is an ABSOLUTE MUST! Without lubrication severe damage can occur.  There is absolutely no reason to feel any kind of discomfort after sexual activity when applying a lubricant is so easy but there are several things you need to know. Some lubricants can be harmful and some just don't work as well as others. 
Oil based products have been used as lubricants for a very long time. Things like Vaseline and baby oil are petroleum based. The first problem is that they leave a coating on the vaginal wall that is very hard to get rid of - thus increasing the chance of bacteria and other infections. The second problem using an oil based lubricant is that the chemicals break down and destroy latex condoms, dental dams, gloves, diaphrams, cervical caps, sponges, as well as the protective coatings around some IUDs and any sexual device made of latex. This can also apply to body oils and creams which are never very good lubricants because they are absorbed into the skin too fast. If oil based lubes are your absolute preference just be aware of the limitations.
The best all-purpose lubricants are water-based and especially formulated to be non-irritating. Once again, buying a lubricant is going to come down to personal preference - some provide light lubrication and some heavy lubrication. Water-Based lubes use two main ingredients: Water and Glycerin. Since the main ingredient is water, water-based lubes do tend to dry up quickly. Make sure to keep a water spray bottle handy to reactivate the lube when it dries up. If lubricants are going to end up in your mouth then a flavored lubricant is what you might consider buying. Some flavored lubricants are for external use only and should not be used inside the vaginal tract. If you intend to use flavored lubricants during intercourse, read the ingredients to see if it contains sugar. Sugar can cause infections inside the vaginal tract. Water-based Lubes clean up with soap and water. 
The newest lubrication products on the market are silicone based. While they make a great body lubricant they also appear to cause damage to some silicone adult toys so your best choice if you are using any silicone products is to stick with water-based lubricants. Like Water-Based lubes, Silicone-lubes can be safely used with all condoms. Silicone-Based lubes are excellent to use because they do not dry up like Water-Based lubes do.  Silicone-based lubes are a bit harder to clean up, but a little extra soap and water does the trick.
As previously stated "Never Every Try Any Anal Penetration Without Using A Lubricant". If you are practicing safe sex oil based lubes are out of the question and you should consider using heavy water based lubricants. 
Both Oil based and Silicone based lubricants can damage adult toys. Either use a water-based lube or protect your toys with a condom.
Glycerin is a type of sugar and can cause yeast infections in women who are especially prone to them. Consider using organic lubricants such as Sensua or Oh! My Lubricant.
There are many lubricants on the market  - once again this is going to come down to personal preference but always do a sensitivity test on your inner arm or inner thigh first before using a lubricant for the first time.

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