Many things can affect how your body responds to a symptom and what kind of care you may need. These include:

• Your age. Babies and older adults tend to get sicker quicker.
• Your overall health. If you have a condition such as diabetes, HIV, cancer, or heart disease, you may need to pay closer attention to certain symptoms and seek care sooner.
• Medicines you take. Certain medicines, such as blood thinners (anticoagulants), medicines that suppress the immune system like steroids or chemotherapy, or natural health products can cause symptoms or make them worse.
• Recent health events, such as surgery or injury. These kinds of events can cause symptoms afterwards or make them more serious.
• Your health habits and lifestyle, such as eating and exercise habits, smoking, alcohol or drug use, sexual history, and travel.

If you're not sure if a fever is high, moderate, or mild, think about these issues:

With a high fever:

• You feel very hot.
• It is likely one of the highest fevers you've ever had. High fevers are not that common, especially in adults.

With a moderate fever:

• You feel warm or hot.
• You know you have a fever.

With a mild fever:

• You may feel a little warm.
• You think you might have a fever, but you're not sure.

Certain health conditions and medicines weaken the immune system's ability to fight off infection and illness. Some examples in adults are:

• Diseases such as diabetes, cancer, heart disease, and HIV/AIDS.
• Long-term alcohol and drug problems.
• Steroid medicines, which may be used to treat a variety of conditions.
• Chemotherapy and radiation therapy for cancer.
• Other medicines used to treat autoimmune disease.
• Medicines taken after organ transplant.
• Not having a spleen.

Symptoms of difficulty breathing can range from mild to severe. For example:

• You may feel a little out of breath but still be able to talk (mild difficulty breathing), or you may be so out of breath that you cannot talk at all (severe difficulty breathing).
• It may be getting hard to breathe with activity (mild difficulty breathing), or you may have to work very hard to breathe even when you're at rest (severe difficulty breathing).

Severe trouble breathing means:

• You cannot talk at all.
• You have to work very hard to breathe.
• You feel like you can't get enough air.
• You do not feel alert or cannot think clearly.

Moderate trouble breathing means:

• It's hard to talk in full sentences.
• It's hard to breathe with activity.

Mild trouble breathing means:

• You feel a little out of breath but can still talk.
• It's becoming hard to breathe with activity.

Pain in adults and older children

• Severe pain (8 to 10): The pain is so bad that you can't stand it for more than a few hours, can't sleep, and can't do anything else except focus on the pain.
• Moderate pain (5 to 7): The pain is bad enough to disrupt your normal activities and your sleep, but you can tolerate it for hours or days. Moderate can also mean pain that comes and goes even if it's severe when it's there.
• Mild pain (1 to 4): You notice the pain, but it is not bad enough to disrupt your sleep or activities.

It is easy for your diabetes to become out of control when you are sick. Because of an illness:

• Your blood sugar may be too high or too low.
• You may not be able take your diabetes medicine (if you are vomiting or having trouble keeping food or fluids down).
• You may not know how to adjust the timing or dose of your diabetes medicine.
• You may not be eating enough or drinking enough fluids.

An illness plan for people with diabetes usually covers things like:

• How often to test blood sugar and what the target range is.
• Whether and how to adjust the dose and timing of insulin or other diabetes medicines.
• What to do if you have trouble keeping food or fluids down.
• When to call your doctor.

The plan is designed to help keep your diabetes in control even though you are sick. When you have diabetes, even a minor illness can cause problems.

Temperature varies a little depending on how you measure it. For adults and children age 12 and older, these are the ranges for high, moderate, and mild, according to how you took the temperature.

Oral (by mouth) temperature

• High: 40°C (104°F) and higher
• Moderate: 38°C (100.4°F) to 39.9°C (103.9°F)
• Mild: 37.9°C (100.3°F) and lower

A forehead (temporal) scanner is usually 0.3° C (0.5° F) to 0.6° C (1° F) lower than an oral temperature

Ear temperature

• High: 40.5°C (104.9°F) and higher
• Moderate: 38.5°C (101.3°F) to 40.4°C (104.7°F)
• Mild: 38.5°C (101.3°F) and lower

Armpit (axillary) temperature

• High: 39.8°C (103.6°F) and higher
• Moderate: 37.8°C (100°F) to 39.7°C (103.5°F)
• Mild: 37.7°C (99.9°F) and lower

Symptoms of a severe allergic reaction can start within minutes of eating or being exposed to an allergen. While symptoms usually occur within 2 hours, in rare cases the time frame can vary up to several hours after exposure. Do not ignore early symptoms. When a reaction begins, it is important to respond right away.

• Skin: hives, swelling (face, lips, tongue), itching, warmth, redness
• Respiratory (breathing): coughing, wheezing, shortness of breath, chest pain or tightness, throat tightness, hoarse voice, nasal congestion or hay fever-like symptoms (runny, itchy nose and watery eyes, sneezing), trouble swallowing
• Gastrointestinal (stomach): nausea, pain or cramps, vomiting, diarrhea
• Cardiovascular (heart): paler than normal skin colour/blue colour, weak pulse, passing out, dizziness or lightheadedness, shock
• Other: anxiety, sense of doom (the feeling that something bad is about to happen), headache, uterine cramps, metallic taste

A severe reaction can take place without hives, so make sure to look out for all of the signs of an allergic reaction.

Symptoms of a heart attack may include:

• Chest pain or pressure, or a strange feeling in the chest.
• Sweating.
• Shortness of breath.
• Nausea or vomiting.
• Pain, pressure, or a strange feeling in the back, neck, jaw, or upper belly, or in one or both shoulders or arms.
• Light-headedness or sudden weakness.
• A fast or irregular heartbeat.

For men and women, the most common symptom is chest pain or pressure. But women are somewhat more likely than men to have other symptoms, like shortness of breath, nausea, and back or jaw pain.

Symptoms of serious illness may include:

• A severe headache.
• A stiff neck.
• Mental changes, such as feeling confused or much less alert.
• Extreme fatigue (to the point where it's hard for you to function).
• Shaking chills.