In general, any allergic reaction will worsen with continued exposure to the offending agent. Anaphylaxis will most certainly progress to death if untreated, and the same is true for the severe allergic reactions such as Stevens-Johnson syndrome and toxic epidermal necrolysis.

• Stevens-Johnson syndrome starts with a generalized macropapular rash, that will then progress to bullae, mucous membrane ulcerations, conjunctivitis, fever, sore throat, and fatigue.
• Toxic epidermal necrolysis will progress similarly to Stevens-Johnson syndrome, but will also cause large layers of the epidermis to detatch from the layers below, leading to extreme amounts of sloughing of the skin surface, and an appearance of the skin that looks like burns or scalding.