DEFINITION
An allergy, otherwise referred to as an allergic or hypersensitivity reaction, is a reaction of an individual’s immune system to foreign substances that are usually tolerated well. In simpler words, it is an isolated dysregulation of the immune system, which recognizes an innocuous substance as a potential threat, and launches a reaction against it that can range from mild to life-threatening.

EPIDEMIOLOGY AND CAUSES-THE HYGIENE HYPOTHESIS
Allergies are diagnosed in increasing numbers and are primarily found in the industrialized world. Recent studies have reported that up to 50 million individuals in the United States either do or will, at some point of their lives, exhibit a type of allergic reaction.

So far, an accurate answer as to why allergies occur does not exist. A certain genetic tendency towards an allergy has been proposed and is considered as a valid claim, but it does not mean that allergies are a genetic trait. It simply means that if a parent has a known allergy, their offspring are more likely (approximately 30%) to develop an allergic reaction themselves. Another theory has been proposed by researchers, called the “Hygiene hypothesis”. This theoretical suggestion proposes that the urban lifestyle has caused less contact with substances such as pollen or plants during childhood, and considerably less contact with microbes. This has lead to an “untrained” immune system which tends to recognize harmless substances as dangerous threats, because, during its maturation in childhood, it has not had many stimuli in order to properly develop.

COMMON ALLERGENS
The substances that trigger an allergic reaction are called allergens and greatly vary. However, some of the most frequent allergens include pollen, grass, nickel and other metals, dust, pet hair or saliva, drugs, eggs and nuts. In reality, an allergy is a process so individualized, that a patient can be allergic to practically anything, ranging from food ingredients to fabric softener and mold.

PRESENTATION
An allergy can manifest in various ways; some less severe, some others can cause a reaction that will possibly endanger the patient’s life if left untreated.

Allergic rhinitis
Rhinitis is, strictly speaking, an inflammation of the nose. An allergic rhinitis, commonly known as hay fever, is a type of allergy, usually caused by inhaled allergens (dust, pollen, etc.) that leads to a flu-like condition with runny nose, blurry or red eyes and cough. Nasal congestion is often debilitating and the discharged material is clear, as opposed to a bacterial infection (white/gray/green). Sometimes, due to the congestion of both the nose and the sinuses, dark-colored circles appear in the area under the eyes- these are known as allergic shiners.

Urticaria
Urticaria is a scientific term for hives. Urticaria appears due to food and drug allergies, but can also develop when an individual touches a substance they are allergic to, or when stung by an insect. It involves reddish wheals that appear on the skin that usually itch.

Contact dermatitis
Another type of rash that may involve scales or blistering due to coming in contact with an allergen. Contact dermatitis is usually limited to the region of the body that has been in direct contact with the substance.

Swelling
Swelling, scientifically referred to as edema, can accompany any type of allergy and can be seen on the skin. Urticarial or rash may be found on a body part that is also swollen; swelling can appear on the eyes and mouth, as in the case of a food allergy. Swelling of the larynx due to an allergy is an extremely dangerous medical emergency, discussed below.

Asthma
Asthma is a condition that, in the majority of the cases, is caused by an allergy. It causes coughing, dyspnea, chest tightness and quick breathing. Common allergens that result in asthma include pollen, dust, mold spores and animal hair or cockroach feces.

Gastrointestinal symptoms
Ingesting food one is allergic to can lead to other symptoms, except for a rash or urticaria. Symptoms from the gastrointestinal tract include vomiting or diarrhea.

ANAPHYLAXIS
Anaphylaxis is a severe, life-threatening allergic reaction, which can cause failure of multiple systems in the human organism and can arise from ingesting food or medications one is allergic to, insect bites, or coming to contact with an allergen. Anaphylaxis develops quickly after contact with the allergen and causes skin reactions (rash, urticaria, itching), tachycardia (a rapid pulse), a drop in blood pressure which can lead to fainting and, most importantly, inability to breathe properly because the throat is swollen. A swollen throat implies that, if not treated properly, anaphylaxis can lead to severe hypo-oxygenation and death. Nausea and vomiting can also be present.

WHEN TO SEEK TREATMENT
Allergic reactions can be mild or severe. Skin rashes that do not progress to dyspnea, cough or chest tightness and are relieved by simple anti-allergic medications such as antihistamine medications (over-the-counter), are usually not dangerous. However, given the fact that it cannot be predicted how an allergic reaction will develop, if you believe you are experiencing allergy-induced symptoms, so contact your doctor right away. If you happen to ingest a food or medication you have not consumed before and gastrointestinal, skin or throat symptoms appear, do contact your doctor immediately. In addition, if you notice a rash or irritation, that recurs after a certain activity, do call your doctor to set up an appointment. If anaphylaxis-like symptoms develop, stay as calm as possible and call 911. If you have experienced anaphylaxis before and know what you allergic to, ask your doctor to prescribe an adrenalin-filled pen, with which you can inject yourself when it happens again.

WORKUP
Allergies can be diagnosed by your physician by means of a detailed medical history, a diary of your daily habits including consumption of food groups and other activities, blood and skin prick tests.

TREATMENT
Allergies cannot really be treated. Various medications, such as antihistamine drugs and cortisone are administered to provide symptom relief. The best way to not get an allergy, is to strictly avoid the allergen, if you know which substance you are allergic to.

POPULAR MISCONCEPTIONS ABOUT ALLERGIES
• I know I have a nut (or other) allergy, but I usually develop a small rash and nothing more. It is safe for me to consume nuts in a limited quantity. Allergies are often dynamic in terms of clinical presentation. Many people experience worsening of their allergies as the years go by and therefore, it is not safe to consume products with ingredients you know you are allergic to, or ingesting medications you are allergic to; at some point of time, a mild allergy may develop into a severe reaction.

• I have heard that allergies are inherited. No. If you have a parent who is allergic to something, it does not mean that you will inherit the allergy. It simply means that you are more likely to develop an allergy, but not necessarily the same.

• If I have an allergy, I will always be allergic to that substance. Allergies can disappear over time, even though it is unknown why. At any case, it is not safe to consume something you know you are allergic to just to see if you still have this specific allergy.

• I am allergic to cats. That is why I stay clear of all animals. Being allergic to an animal means that you are allergic to their dander. This does NOT mean you are allergic to all pets or animals. There are people who are allergic to different breeds of dogs, for instance. Contact your allergologist or dermatologist to detect your allergies.