Many people are well aware if they’re having an allergic reaction to something, but often the clues are much more subtle. If your reaction is mild, delayed, or from an allergen you’re exposed to repeatedly, you may mistake it for something else. Here are ten telltale signs that indicate an allergic reaction.

1. Rash. This may vary from a simple redness on the skin, or can be more severe and include bumps, swelling, blistering, or hives.

2. Itching. This can be a mild annoyance or more severe and is often associated with a rash.

3. Breathing troubles. Someone having an allergic reaction may have difficulty breathing or even an inability to breathe. In many people with asthma, the normal asthma symptoms may be triggered by exposure to an allergen. Breathing difficulties may also include wheezing and coughing.

4. Eye problems. Itchy, watery and bloodshot eyes are often a good indicator of an allergic reaction.

5. Swelling. Swelling of the face and tongue is a common and dangerous symptom of an allergic reaction. While some facial swelling isn’t a problem, if the tongue becomes too swollen, it can block your airway and prevent proper breathing, causing the person to suffocate.

6. Headache. In addition to facial swelling, swelling in the head may also cause headaches. They can also be caused by blockage in the sinuses from a stuffy or runny nose.

7. Nasal symptoms. Depending on the person, nasal symptoms may vary from a runny to stuffy nose, or sneezing.

8. Stomach problems. Digestive symptoms can vary from a simple mild stomach ache to extreme pain, vomiting, and severe or bloody diarrhea.

9. Shock. This is a symptom experienced when your blood pressure drops dangerously low and your internal organs aren’t getting enough oxygen to function properly. This is a very serious symptom and is usually characterized by confusion, anxiety and eventually loss of consciousness. The person’s skin color can vary from pale white to red and they may or may not be sweating.

10. Anaphylaxis. This isn’t really a symptom in itself, but is a term used for any combination of the other symptoms that comes on very quickly and is life-threatening. This often includes shock and should be treated immediately.

The only way to be sure that you have an allergy is to see a doctor. Be sure to keep track of all your symptoms, when they occur, and anything that might be related. Your doctor will use this information to take a best guess of what he thinks the problem is and may perform allergy skin prick tests with small amounts of allergens.

Using the results, your doctor will recommend a treatment specifically designed for your symptoms which may include a simple antihistamine, or an epinephrine pen for more severe symptoms. They may also be able to get rid of your allergies using a series of shots, depending on your symptoms and their severity.