As we already learned, allergic reactions are linked to allergen IgE; mast cells, basophils, and chemical mediators that induce almost immediate allergic symptoms (early or immediate phase reaction).  Typically, sneezing, a runny nose, nasal congestion, and itching of the nose, throat, or wheezing peaks rapidly, but subsides within a few hours.  However, as we’ve come to learn, some patients can also experience a so-called “late or delayed reaction” after immediate allergic reaction.

The delayed reaction usually appears about four to six hours after allergen exposure, and, in some cases, and up to eight hours after.  A delayed phase reaction is an inflammatory reaction that is caused by chemical mediators, which are released and produced after initial immediate phase reaction.

In some cases, this delayed reaction can actually be more severe than an immediate reaction.  While antihistamines and quick-relief bronchodilators can only effectively control immediate reactions, corticosteroids and allergy shots (immunotherapy) can control delayed reactions.  This is why nasal steroid and inhaled corticosteroids play a significant role in decreasing inflammation in allergic rhinitis and asthma.

Both patients and physicians have noted a phenomenon termed “priming.”  Priming is caused by prolonged exposure to allergens, which induces the cells and tissue to become hypersensitive.  Therefore, it takes less pollen in the air to initiate an allergic reaction late in the pollen season than it did at the beginning of the season.  Symptoms can also be triggered by other allergens that do not normally trigger an allergic response, or even by irritants such as pollutants, smoke, powders, cosmetics, and newsprints.