A runny nose, cough and itchy eyes are all too familiar for those who suffer from allergies. Maybe you get frequent colds as well. Millions of people suffer from these symptoms, and many go to the medicine cabinet for relief. How do decongestants and antihistamines work? Are they the same thing? How do they affect the body? Are they safe? Let’s get the answers to these questions and more.
How an Allergic Reaction Occurs
Even though allergies are bothersome, they are actually the result of an exaggerated natural biochemical process. Our bodies come into contact with particles in the environment every day. Collectively these particles are called allergens. They could be animal dander, dust, mold, plant particles, pollen or pollution.
When your body encounters an allergen for the first time, T-cells in your immune system begin to produce substances like cytokines and interleukins. These substances stimulate other immune cells (B-cells) to create antibodies (IgE) which help to get rid of the allergen. Your immune system also has a “memory,” which means this process happens much faster the next time the allergen appears.
For some reason that scientists don’t fully understand, the IgE antibodies can cause reactions in your body that lead to allergy symptoms. This is largely affected by the release of histamine and other chemical mediators from special white blood cells. In some cases, the reaction may be due to exposure to something harmless in the environment like pollen. The end results are symptoms like:
- Mucous secretion (runny nose)
- Nerve irritation (can cause itching)
- Vasodilation (opening of the blood vessels which makes the nose lining leaky and swollen)
- Smooth muscle contraction (can cause wheezing or cough)
Now that we understand how allergies occur, this helps explain how common remedies work to relieve allergy symptoms.
How Decongestants Work
One of the main causes of allergy symptoms is vasodilation (widening of blood vessels) in the lining (mucous membrane) of your nose, sinuses and upper airways. This leads to a runny nose and congestion. In general, decongestants cause the small blood vessels to become narrower which reduces the swelling and thickness of the mucous membrane.
Decongestants can come in pill or nasal spray form. The sprays act directly on blood vessel cell receptors (α1 and α2 adrenergic receptors), which leads to the constriction of the blood vessels. The pills work by a similar mechanism but take a bit longer to work since the drug must circulate through the blood first.
Some common decongestants are:
- Afrin, Dristan, Vicks Sinex (oxymetazoline): nasal spray
- Sudafed PE, Suphedrin PE (phenylephrine): oral medication
- Actifed, Allegra D, Aleve D, Silfedrine, Sudafed, Suphedrin (pseudoephedrine): oral medication
Decongestant Side Effects
Decongestants can have significant side effects, and each one is different:
- Oxymetazoline: Can cause rebound congestion if used for more than three consecutive days; this means you may become dependent on the drug to prevent symptoms
- Phenylephrine: May cause high blood pressure and prostate enlargement; people with anxiety or panic disorders, or on anticonvulsant medication for epilepsy should not take this drug
- Pseudoephedrine: Side effects may include central nervous system stimulation, insomnia, nervousness, excitability, dizziness, anxiety, palpitations, dilated pupils, hallucinations, arrhythmias, hypertension, seizures and ischemic colitis
Anyone with a history of high blood pressure, circulation problems or any kind of heart condition should consult with their doctor before taking a decongestant.
How Antihistamines Work
Earlier we mentioned that allergies cause the release of histamines from special immune cells that react to allergens. Histamines then act on different parts of your body to cause allergic reactions.
Medications that target the H1 histamine receptors in the body are the antihistamines used to treat allergy symptoms. By blocking the H1 receptors, the blood vessels get constricted and tighten up. Since the blood vessels are less leaky, this means less runny nose and congestion. Some common antihistamines are:
- Fexofenadine (Allegra)
- Hydroxyzine (Vistaril)
- Loratadine (Claritin)
- Cetirizine (Zyrtec)
Side Effects of Antihistamines
In general, antihistamines are very safe, but the side effects can be annoying. Some possible side effects due to antihistamines are:
- Dry mouth
- Nausea and vomiting
- Difficulty urinating
- Blurred vision
How Corticosteroids Work
Another common treatment for allergies and hay fever are corticosteroids, typically in the form of a nasal spray. The way steroids work is to decrease inflammation, and allergic reactions are an inflammatory response to allergens.
Side Effects of Steroid Nasal Sprays
Some possible side effects of corticosteroid sprays are:
- Burning, dryness or irritation in the nose
- Irritation of throat and/or sneezing
- Decreased or loss of sensation of taste
Much less common, or if you overuse the spray, you might experience symptoms, such as:
- Bad smell
- Vision problems or eye pain
- White patches or sores inside nose, mouth or throat
- Skin rash
- Muscle pain
- Nausea or vomiting
- Ringing in the ears
- Breathing problems
Some people may be concerned about the possible systemic effects of steroid nasal sprays. Most research has shown this risk to be very low. In one study, 12 healthy volunteers were given the steroid fluticasone as a nasal spray. The dosage given was up to 12 times the normal daily dose. The study did not show any significant systemic side effects.
Still, if you have any health problems, such as diabetes, osteoporosis or immune system disorder, you should check with your doctor before using any kind of steroid medication, including nasal sprays.
What is Anaphylaxis?
Anaphylaxis is a life-threatening allergic reaction that affects your entire body. The symptoms of anaphylaxis include:
- Hives and itching all over your body
- Eye, face and/or throat swelling
- Wheezing and trouble breathing
- Hoarseness, cough or throat tightness
- Tingling or burning in the hands, feet, lips or scalp
- Low blood pressure
In the worst-case scenario, anaphylaxis can lead to respiratory distress, shock or even death. It is a medical emergency and must be treated right away. Doctors usually treat anaphylaxis with epinephrine injections, antihistamines and occasionally steroids.
If you have severe allergic reactions, such as to bee stings, your doctor will prescribe you an epinephrine pen. In the event of exposure to the allergen, you can self-administer an epinephrine injection with the pen. Even if your symptoms subside, you should still see a doctor immediately.
Food Allergy Facts
Certain foods may increase your chances of allergic reactions. For this reason, some experts recommend avoiding these foods:
- Dairy products
- Tree nuts (walnuts, almonds, pine nuts, Brazil nuts and pecans)
- Gluten, including wheat, barley, rye and oats
- Fish and shellfish
- Meat like beef, chicken, mutton and pork
- Seeds, often sesame, sunflower and poppy
- Spices like caraway, coriander, garlic and mustard
Now the list of foods is too long to eliminate everything at once. Instead, try to eliminate one thing at a time and track your symptoms. If you notice no benefit, then move onto the next item on the list. This process takes time, and it helps if you keep a food journal to keep track of your progress.
A food allergy can appear very much like hay fever as far as symptoms are concerned. Gastrointestinal effects like an upset stomach, nausea, vomiting or diarrhea may also be present. In extreme cases, an anaphylactic reaction can occur.
How About Allergy Shots?
Allergy shots, or immunotherapy, basically attempts to put the allergy reaction in reverse. First, you get tested to determine what allergen causes your symptoms. Next, shots that contain the allergen are administered to you. The initial doses are very small, and this is meant to cause a minor reaction in your body that you should not even notice.
Gradually, over time, the dosage of the shot is increased. The process is called desensitization. The idea is that by exposing your body slowly, it gets used to the presence of the allergen without leading to full-blown symptoms. In the end, the allergen has no effect on you at all.
The initial phase of immunotherapy lasts three to six months, and you get injections one to three times per week. After this buildup phase, you enter into a maintenance phase where you receive injections once a month for a total of three to five years.
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