We are constantly exposed to the cold virus, primarily through touching things and then rubbing our eyes or noses. Our bodies ward these off all the time as they live in our nasal cavities. Under certain conditions (stress, changes in temperature, whatever) our immune systems fail and we succumb to symptoms.

Unlike, say, chicken pox, it's pretty rare to know exactly who exposed us to any given cold or flu. They're just all around us all the time.

I want to tour this week but ive got quite a bad cold. Im sneezing, eyes are watering and my throats sore.

Am i being a wussy because im thinking about canceling?

Will be clients be pissed off that im sneezing during a booking?

I wouldn't want to work with a full on cold, I don't think it is particularly attractive.
As soon as move your head down, it tends to bring on the sniffing, nothing particularly nice about that.
I have worked with hayfever before, and found the same thing. At least you cant catch hayfever though.