The human immune system responds to a substance that is not harmful to the body, which are ubiquitous in nature. The substances that cause a response are called allergens.
The human immune system responds to substances that do not harm the body, which are common in nature, which is the substance that causes the response called allergens.
immune system of the human response to substances that are not harmful to the human body which is common in the natural substances that the response is called allergens