The temperature is rising outside and you're feeling the heat, so you crank up the AC and sit back and enjoy as your place starts to cool off. Before you know it, your wife/daughter/mother (fill in the blank!) begins to complain that she's "FREEZING!" We've all been there, and the battle over the air conditioner is often no fun. Why is it that women tend to always be colder than men? Several theories abound, though none have necessarily been proven to be ultimate truth.

Muscle Mass

The more muscle mass your body has, the easier it is for it to generate heat. As men tend to have higher muscle mass numbers than women do, they therefore tend to be warmer. Higher metabolisms are also associated with the idea of heat generation and fit into this theory as well. The more muscle, the more blood flow there is. The more blood flow, the more warmth that is generated.

Women Shed Heat Faster

This one requires a bit of math. There is a theory that the body's ability to generate heat is determined by volume (radius cubed), and that heat dissipation is dependent upon the body's skin surface area (radius squared). This basically translates into the following: the smaller your body size, the lower your heat generation/dissipation ratio. Therefore, those with smaller bodies (generally women) tend to be colder.

Vasoconstriction

Women have a higher vasoconstriction threshold temperature.  During vasoconstriction, blood flow to the skin is restricted as the external temperature falls in order to divert blood to internal organs, thus maintaining core temperature. The theory is that as the ambient temperature falls, women shut off blood flow to the skin sooner in order to provide more warmth to their unborn babies, so they feel colder. This idea is both interesting and unproven.

Menstruation

Though unproven, there is a theory that due to the hormonal changes women experience during their menstrual cycles, they may feel colder at particular times of the month.

In terms of temperature differences, it is obviously much easier for the colder person in your household to put on an extra sweater or pair of sweats than it is for the warmer person to start stripping.

Differences in temperature preference is a common issue for those with air conditioners and is sometimes easiest dealt by those who have window unit AC's. In that case, your best bet is to split up: the warmer person can hang out in the cool, AC-pumping room, and the colder person can "chill out" in another room, either without the AC window unit on or at a lower power setting. Compromise is key!