These effects might range from minor discomforts to fatal outcomes depending on the type of antigen antibody reaction and the previous exposure to the same antigen. Thus, in order for someone to develop hypersensitivity, they should be sensitized in a previous exposure. At the same time, development of a clinical manifestation might be due to different types of hypersensitivity reactions as there are four types being described in the literature. Therefore, when a skin reaction manifest, it may be due to all four types of hypersensitivities but type I, III and IV are more specific.
Type I Hypersensitivity
Also known as immediate or anaphylactic hypersensitivity, these types of reactions could be seen in the development of urticaria and eczema. It is considered severe in the presence of respiratory involvement as in the case of developing asthma. Furthermore, there may be other organs involved in this type of reactions and the antigen that triggers this type of reactions is said to originate from outside or in other words, are exogenous. The reaction involves release of IgE antibodies and the cellular structures that contribute would mainly be the mast cells. These types of skin reactions said to occur suddenly within 15 – 30 minutes after exposure although a delayed type of reaction is also a possibility.
Type III Hypersensitivity
In this type of hypersensitivity reactions, the process is mediated by IgG and IgM type of antibodies and is also known as immune complex mediated hypersensitivity reactions. Development of Systemic Lupus Erythematosis or SLE can be considered a Type III reaction and the skin manifestations of which include edema and erythema. The antigen that triggers such reactions can originate externally or within the body and it takes about 3 – 10 hours for the manifestations following an exposure.
Type IV hypersensitivity
Many skin related reactions can be classified under this type of reactions and it involves the classical descriptor the tuberculin or mantoux test as well as the occurrence of contact dermatitis. Such reactions would give rise to erythema and indurations in the skin and would be mediated through cellular processes than antibodies. Thus, these reactions are given the name ‘cell mediated’ or ‘delayed’ type reactions as it takes 48 – 72 hours to precipitate from the time of exposure to the antigen.
As you can see, the skin manifestations related to a reaction can be contributed through various mechanisms, although the main contributor will be dependent based on the antigen underlying the condition.