Final answer:
A burn with redness and irritation but without blisters is a first-degree burn. This type of burn only affects the epidermis and typically heals on its own, unlike more severe second, third, or fourth-degree burns that affect deeper layers and require medical treatment.
Step-by-step explanation:
A type of burn characterized by redness and irritation but with no blisters is known as a first-degree burn. This form of burn affects only the outer layer of the skin, called the epidermis, and is considered the least severe type of burn. With a first-degree burn, the skin may be painful and swollen, but these burns generally heal on their own without leaving blisters. Examples include mild cases of sunburn.
It differs from a second-degree burn, which involves the epidermis and the dermis leading to blistering, and a third-degree burn, which extends through every layer of the skin, destroying tissue and affecting sensory function. Lastly, a fourth-degree burn is the most severe, affecting not only all layers of skin but also the underlying muscle and bone.