ALLERGIES

Allergies are an overreaction of the immune system. Exposure to what is normally a harmless substance, such as pollen, causes the immune system to react as if the substance is harmful. Any such substance is called an allergen.

When a person with an overactive immune system is exposed to an allergen,
these events takes place:

1 - The immune system starts to produce a specific type of antibody to fight the allergen.

2 - These antibodies attach to a type of blood cell called a mast cell. Mast cells make and store histamine. The mast cells "patrol" the body, mainly in connective tissue close to the surfaces, including interior surfaces. Mast cells are plentiful in the skin, in the breathing passages beginning with the nose, and in the digestive system beginning with the mouth, both places where allergens tend to enter the body.

3 - The mast cells break apart, releasing a number of chemicals including histamine. Histamine causes widening of capillaries, decreased blood pressure, increased release of gastric juice, fluid leakage forming itchy skin and hives, and tightening of smooth muscles of the bronchial tube and uterus.

So, histamine causes most allergy symptoms, including itchiness, hives, airway congestion and runny nose.

If the allergen is in the air, like pollen or mould spores, the allergic reaction will occur in the eyes, nose, sinus cavities and lungs. If the allergen is taken by mouth, the allergic reaction will occur in the mouth, stomach, and intestines.

Histamine, a neurotransmitter, plays a vital role in the body. In proper amounts, it keeps the brain attentive, alert and awake. It plays other roles as well. It also produces conditions which can help the immune system fight off infection.

Ideally, these conditions are localised to where an infection is present, but in an allergic reaction, the swelling and inflammation are widespread, extreme and unnecessary.

Some antihistamines, particularly the older types, fill up histamine receptors in the brain by fooling the receptors into accepting them as histamine. The brain then gets drowsy. Gravol is marketed as an anti-nausea drug although it is a typical antihistamine. Many parents have been pleased by the Gravol Snooze effect on their children during a road trip. Benadryl has been used as a sedative for infants and children, although some will become restless or hyperactive after taking it.

Newer "non-drowsy" antihistamines are less able to get into the brain tissue, so they don't make you dopey.

Sometimes the old-style antihistamines are preferred because of a more powerful and immediate effect, such as when a serious allergic reaction has to be stopped immediately.

If your feet smell and your nose runs, you've been built upside-down. Sorry.

If a great number of mast cells are triggered to release histamine, there may be an exaggerated reaction throughout the body, such as hives, decreased blood pressure, shock, even loss of consciousness. This severe type of reaction is called anaphylaxis and can be life-threatening.

Mild reactions include those symptoms that affect a specific area of the body such as a rash or hives, itchy, watery eyes, and some congestion. Mild reactions do not spread to other parts of the body.

Moderate reactions include symptoms that spread to other parts of the body. These may include itchiness or difficulty breathing.

An anaphylactic reaction is a life-threatening emergency. It may begin with the sudden onset of itching of the eyes or face and within minutes progress to more serious symptoms, including swelling that can make breathing and swallowing difficult, abdominal pain, cramps, vomiting, and diarrhoea. Mental confusion or dizziness may also be symptoms, as anaphylaxis causes a quick drop in blood pressure. People who are prone to anaphylactic shock should carry a powerful, old-style antihistamine like a benadryl tablet, to be chewed immediately. In a particularly severe reaction, they should be equipped with a special adrenaline (epinephrine) injector. An "epi-pen".
What some of us used to call a "bee sting kit".

Medical attention should be sought immediately.

Most allergies are inherited. When one parent is allergic, the child has a 50% probability of having allergies; 75% if both parents have allergies. The inherited tendency may produce an allergy in childhood or later life. The allergy won't necessarily be to the same allergen(s) as the parent(s) had.