For example, the type of environment (climate, bugs, and soil quality) in which a plant grew will affect it, as will how and when it was harvested and processed.
In many cases, scientists are not sure what specific ingredient in a particular herb works to treat a condition or illness. Whole herbs contain many ingredients, and they may work together to produce a beneficial effect. Many factors determine how effective an herb will be. For example, the type of environment (climate, bugs, and soil quality) in which a plant grew will affect it, as will how and when it was harvested and processed.