Sarah -  The rhesus blood typing system is very similar to the A, B, O system, but it's much more complicated.  There's not just three types, it's actually a lot.  When people talk about Rhesus positive or Rhesus negative they're talking about the Rhesus D gene.  That means that you either have or do not have these particular structures on the outside of your red blood cells.  Rhesus positive means that you do have them and Rhesus negative means that you don't have them.  He's exactly right that Rhesus positive is dominant.  The allele for that is dominant over the Rhesus negative allele.  Actually about 84% of the UK population is Rhesus positive.

Ben -  So that again (as with the A, B, O system) means that if you have two parents that are Rhesus negative then you're certainly going to be Rhesus negative, but if your parents are Rhesus positive then actually you could turn out to be either.

Sarah -  Yes. Both of my parents are Rhesus positive but I'm Rhesus negative.

Ben -  That means we can work out that each of your parents has one copy of the gene saying Rhesus positive and one saying Rhesus negative in order to have passed on the negative ones to you.

Sarah -  Yep!

Sarah -  This is linked to what I was saying before about thermo-regulating.  Your body works best at a certain temperature around 37 degrees centigrade so when your temperature goes below or above that your body will try and reset it to its level at homeostasis.  When you're too hot you do things like you sweat and when you're cold you shiver to warm you up.  The simple answer is that it takes a lot more energy to warm yourself up because to do that with shivering it's kind of like going to the gym.  It's the really fast contracting of your muscles that causes you to shiver.  It's like going for a run or doing other sorts of exercise.  Obviously that's going to take up a lot of energy whereas cooling yourself down through sweating is a much more passive process.  It doesn't take that much energy from your body to pump the sweat out onto your skin so the air is sort of doing the work for us to cool us down.

Ben -  So as your sweat evaporates off your skin that takes the heat away from you, you're not having to actively remove the heat.

Sarah -  Exactly.

Ben -  But Steve is in Dubai.  Surely the processes that people go through in Dubai can't be the same as over here in the UK where, let's face it, it's not very warm.

Sarah -  No. I think also not just the heat but the level of humidity in the air is quite important.  If it's really humid so there's lots of water already in the air it's obviously going to be a lot harder for the moisture in your skin to evaporate so you will always feel hotter when it's humid than when it's dry.

Ben -  The same amount of sweating will actually lead to less cooling.

Sarah -  Yes, because the air is already too full of water for it to take much more from your skin.

Sarah -  Well, he did say normally I get quite cold when I go to sleep and that's quite normal because your body temperature actually drops during the night and it's usually at its coldest about two hours before you get up.  But when you've been drinking your liver is madly metabolising all the alcohol, breaking it down to get it out of your blood stream.  This is a really exothermic process which means it produces a lot of heat.  Your liver is actually the main heat-producing organ in your body anyway.  When it's working extra hard you're producing a lot more heat than usual.  Added to that alcohol stops you from being able to thermo-regulate.  When you're too hot or you sweat to cool down you should be able to warm up - the alcohol stops your body from being able to do that.  This combined with much more heat being produced by your liver really makes you heat up in the night.

Ben -  So it's a double whammy then.  The actual breaking-down of the alcohol produces more heat anyway and the fact that there's alcohol there means your body can't cope with that excess heat?

Sarah -  Yeah, exactly.  Although you can actually see the opposite thing in people coming out of clubs late at night.  I'm sure everyone's seen it or done it themselves: the sort of 'beer jacket' effect where you come out in a just a small T-shirt and you're not cold.  It's because the alcohol makes you less-able to feel the cold.

Ben -  This is for when you've gone out and tried to avoid spending the extra pound to put your coat in the cloakroom so you just leave your coat at home.  Actually at 3am, you don't notice at all that you're losing lots of heat?

Sarah -  Exactly.  Usually it's fine but it can be quite dangerous for people who live on the street and if they drink they might not notice it's really cold so it can be quite dangerous for them.