Define chemical barriers of birth control.

Explanation

**Step-by-Step Solution:**

1. **Definition of Chemical Barriers**: Chemical barriers in birth control refer to contraceptive methods that utilize chemical substances to prevent pregnancy. These methods act as barriers to sperm, either by killing them or inhibiting their movement.

2. **Types of Chemical Barriers**: There are various types of chemical barriers available. The most common include spermicidal agents, which can be found in forms such as tablets, gels, and creams. These substances are applied in the vagina before intercourse to kill sperm.

3. **Mechanism of Action**: The primary function of these chemical barriers is to create an environment that is hostile to sperm. For instance, spermicidal agents disrupt the sperm's ability to swim and reach the egg, thus preventing fertilization.

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