You're right. More pesticides can get into your skin if you are sweating. I'm not so sure about germs though. Sweat and skin temperature affects how quickly pesticides get into your skin. This is why it is always good to wear clothing that covers your skin during and after spraying.

Yes, certain chemicals and can be absorbed through the skin.Germs usually are blocked by the skin, but can enter your body through small cuts or scrapes (and of course through your nose, mouth, etc.). If you look at this site:
http://www.nceas.ucsb.edu/~burton/index.html
You can see a picture of me dressed up to avoid getting hantavirus. A person working with dangerous chemicals should also wear protective clothing. (You don't even have to be sweating for the substances to get in.) You might want to find out about specific pesticides, because they vary a lot in their toxicity and ability to penetrate skin. There are federal laws about what can be used and what precautions workers must take. For more information, you would need to find the name of the specific chemicals.

Here are some sites on pesticide safety :
http://www.cas.psu.edu/docs/CASDEPT/Hort/TFPG/part3/part31e.htm
http://ohioline.ag.ohio-state.edu/b750/b750_3.html

thanks for asking.

When your pores open up it's not like direct pathways open to your body's insides (i.e. bloodstream), as in an open wound, but it's sort of like inhaling a substance. Once something gets into your pores (or your lungs) your body may not react to it if it's a substance that doesn't react with compounds in these areas or it may cause an adverse reaction if the substance is reactive. If germs were to enter the body through a wound it would likely cause an infection, whereas if germs enter your body through your pores it is not likely to cause an infection. However, this greatly depends on the type of germ you are talking about. Germs have very specific actions. For example viruses have evolved to attack one specific cell type in one specific organism. If the virus can't get to that cell type (because it is in the pores of your skin) then it will not cause an infection. Bacteria also have very specific living requirements. If the environment of the pore is not suitable to the bacteria then it will not be able to infect you. In a sense having your pores open up isn't like walking around with a bunch of open wounds on your body is.
Once things (like germs or pesticides) get into the bloodstream they can do much more damage. Not everything absorbed via the pores will get into the bloodstream because there is still a barrier (the pore wall). However, pesticides are not life forms. They don't have specific living requirements. They are just compounds that will either react or not react with the other compounds in the immediate vicinity. So some pesticides are not harmful to humans at all. Other pesticides can be very reactive with compounds in humans and therefore cause very adverse reactions. Think of it like germs are life forms (not entirely because viruses are not technically life forms) that won't to replicate themselves and they need to live inside your body in order to do this. When this occurs it is usually harmful to us in some way, i.e. we get a cold, or the flu, or AIDS. Pesticides are merely chemical compounds that will react with other chemical compounds if they are able to and sometimes the products that are formed in these reactions are toxic to us. So if the reactions happen in our bodies or nearby we can be adversely affected by pesticides.