Allergies occur when your body has an immune response to something in your environment. When you’re allergic to something, your body mistakes it for a foreign invader, like a flu virus. This can cause cold-like symptoms. Many people have allergies to both indoor and outdoor substances, such as pet dander, pollen, and dust mites. Allergies can be seasonal or last all year long. They can cause an irritating inflammation in your nose that may give you a tickly, itchy feeling.