Preservatives are a type of food additive added to food to prolong shelf life and keep products from being spoiled by mold, bacteria, and yeast .
Many preservatives are made out of synthetic chemicals which our bodies are not designed to process and digest. It may be common sense that ingesting chemicals would not be good for your health, however many studies have been done on the effects of long-term use.
Other countries have gotten smart and have banned the following products:
Bread with Potassium Bromate
The use of potassium bromate as an additive to commercial breads and baked goods has been a huge contributor to bromide overload in Western cultures. Bromated flour is "enriched" with potassium bromate. Studies have linked potassium bromate to kidney and nervous system damage, thyroid problems, gastrointestinal discomfort, and cancer. Use of potassium bromate is banned in Canada, China and the EU. 
Preservatives BHA and BHT
BHA (butylated hydroxyanisole) and BHT (butylated hydroxytoluene) are commonly used preservatives. BHA is known to cause cancer in rats, and may be a cancer-causing agent in humans as well. US experts concluded that BHA "is reasonably anticipated to be a human carcinogen." BHA and BHT are banned in Japan and parts of the European Union, and the UK does not permit BHA in baby foods. 
These are just a few examples of the hundreds of chemicals used in processed foods. Here is what you can do to start reducing your intake of preservatives and minimize their effects on your health.
1. Replace processed foods with fresh foods. Stick to the produce section of the supermarket.
2. Buy organic as much as possible
3. Learn the art of canning food without preservatives
4. Do a detox seasonally to release toxicity from the body