How does nicotine get in, where does it go, and how long does it stay?

When you inhale smoke, nicotine is carried deep into your lungs. There it is quickly absorbed into the bloodstream and carried throughout your body. Nicotine affects many parts of the body, including your heart and blood vessels, your hormones, the way your body uses food (your metabolism), and your brain. Nicotine can be found in breast milk and even in mucus from the cervix of a female smoker. During pregnancy, nicotine freely crosses the placenta and has been found in amniotic fluid and the umbilical cord blood of newborn infants.
Different factors affect how long it takes the body to remove nicotine and its by-products. In most cases, regular smokers will still have nicotine or its by-products, such as cotinine, in their bodies for about 3 to 4 days after stopping.