What route involves injecting a drug into the dermal layer for purposes such as allergy testing?

The route that involves injecting a drug into the dermal layer is known as the intradermal route. This technique places the medication just below the outer layer of skin, which is particularly useful for applications such as allergy testing and certain vaccinations. The intradermal injection allows for a localized response that can be easily observed, as well as a slower absorption of the drug into the bloodstream compared to other routes. The formation of a small wheal or bump at the injection site indicates that the drug has been successfully introduced into the dermis, allowing healthcare providers to assess the body's reaction to allergens or other substances effectively.

In contrast, other routes, such as intramuscular, subcutaneous, and intravenous, involve deeper layers of tissue or directly into the bloodstream, which do not provide the same localized reaction needed for allergy testing.