Allergies are a common problem that affects many people around the world. The severity of allergic reactions can vary from mild to life-threatening. To describe the severity of allergies, we can use a variety of synonyms such as lethality, harm, danger, peril, and toxicity. The deadliness of allergies can also be expressed as potency, strength, severity, intensity, and power. These words can convey the seriousness of allergic reactions and the potential harm they can cause. It is important to take allergies seriously and seek medical attention when necessary to prevent any potential harm or danger.