Your skin is your largest organ, and it does a very good job of protecting everything inside you. Some products are caustic enough to damage your skin but very few are absorbed into your body.
What to do
Washing with soap and water is the most important treatment for every skin exposure. For irritating or corrosive substances the initial gentle washing should be followed by irrigation with copious amounts of running water.
Soaking the affected area in still water may prolong the exposure rather than removing the substance from the skin.
How long to do it
Most skin exposures only need a simple wash and rinse, but some (eg, drain openers) may need longer irrigation and some (eg, super glue, jalapeno peppers) may need more than just washing. Call poison control (800-222-1222) for specific recommendations.
Don’t try to neutralize an acid by adding baking soda, or an alkali by adding vinegar. Neutralization is a powerful chemical reaction that breaks molecular bonds and releases energy in the form of heat; this can be more damaging than the original exposure. The proper treatment for these exposures is irrigation with copious amounts of running water. Begin irrigation immediately and call poison control for advice on what to do next.
What to expect
This is highly variable and depends on the product, but most household products have mild effects, if any.
Getting medical care
Generally speaking, medical care is needed for skin exposures that result in injury or pain, especially if the face, hands or genitals are involved. There are a few products that have special risks or need specific treatment, but always start with irrigation.