Why does my doctor want me to do a food challenge when my blood test showed negative for a shellfish allergy?

DEAR DOCTOR K: Last month I broke out in hives after eating oysters. I had a blood test, which came back negative for a shellfish allergy. Why does my doctor still want me to do a food challenge?

DEAR READER: Allergic reactions occur when your body's immune system overreacts against a harmless substance -- in your case, possibly, shellfish. Food allergies can cause a variety of symptoms that range from mild to life-threatening.

What medications will make allergy season more bearable?

DEAR DOCTOR K: This year I'm suffering from seasonal allergies for the first time. What medications will make allergy season more bearable?

DEAR READER: Sneezing; itchy, runny, stuffy nose; red, itchy, watery eyes; sore throat. Hay fever can cause great misery. If misery loves company, you'll be pleased to know that I and millions of other people suffer from hay fever. Luckily, many medications can help treat its symptoms.

What can I do for terrible sinus headaches?

DEAR DOCTOR K: I get terrible sinus headaches during allergy season. Antihistamines help, but not completely. What else can I try?

DEAR READER: I see many patients during allergy season complaining of sinus headache pain. It occurs most often in the center of the face, the bridge of the nose and the cheeks. And it's sometimes accompanied by nasal congestion and clear or opaque nasal discharge.

Is dust dangerous?

DEAR DOCTOR K: I keep a tidy house, but no matter how much I clean, there's more dust than I'd like. Is dust dangerous to my family's health?

DEAR READER: Yes, depending on its contents, dust can be harmful to your health. What is dust? It's a little like sausage: You don't want to know what's in it. But I'll tell you anyway.

When should I start giving my baby solid foods?

DEAR DOCTOR K: When should I start giving my baby solid foods? Will starting solids too early increase her risk of food allergies?

DEAR READER: Breast milk or iron-fortified infant formula provides all the nutrients your baby needs for the first 6 months. Most pediatricians I know do not recommend starting solid foods before 4 months. The introduction of solid foods before 4 to 6 months may not provide the proper balance of nutrients -- and it may increase the risk of your infant's developing food allergies.

Can I suddenly become allergic to shellfish?

DEAR DOCTOR K: I recently ate shrimp and broke out in hives. This has never happened before. Could I have developed a new food allergy as an adult?

DEAR READER: Yes, you can, and it's not that unusual. Allergic reactions are overblown immune responses against a harmless substance — in some cases, a food. Food allergies are most prevalent in childhood, but even if you escaped them then, you're not necessarily off the hook. You can develop allergies at any point in your life, and fish and shellfish allergies are more likely than others to begin in adulthood.

What should I know about allergic reactions?

DEAR DOCTOR K: My sister-in-law has a bee-sting allergy. What happens if she gets stung? Can it be life-threatening?

DEAR READER: For someone with such an allergy, a sting can be very serious — yes, even life-threatening. If left untreated, an allergic person could die within minutes to hours after a bee sting. Bee-sting allergies — along with some other allergies, which we'll discuss — are so serious because they can lead to anaphylaxis, a severe, sometimes life-threatening, allergic reaction. It occurs within minutes of exposure to an allergy-causing substance (allergen). It is also sometimes called anaphylactic shock.

Is there a treatment for lactose intolerance?

DEAR DOCTOR K: I've recently become lactose-intolerant. Is there a treatment for this? Or do I have to say goodbye to cheese and milkshakes forever?

DEAR READER: Yes, there is a treatment. But whether it will allow you to eat cheese and drink milkshakes occasionally depends on your gut. Lactose intolerance occurs when your gut does not have enough of an enzyme called lactase. Lactase breaks down lactose, the main sugar in milk. When lactose isn't properly broken down, it can cause abdominal cramping, bloating, gas and diarrhea.

How is a shellfish allergy diagnosed?

DEAR DOCTOR K: I've always loved shellfish. But lately when I eat it, I break out in hives. Could I be allergic?

DEAR READER: You sure could be. Such an allergy could cause more symptoms than just a rash, including low blood pressure and difficulty breathing, so you need to find out if you are allergic to shellfish. See an allergist, a doctor who specializes in diagnosing and treating allergies.