How to Differentiate between Skin Allergy and Skin Disease

Skin is the largest organ in the body and is subjected to many insults as well as disease manifestations. Due to its external location, we tend to see changes accordingly in the skin which might be reflected in the mucosal surfaces of the internal organs as well. Some of these changes would be linked with skin conditions such as dermatitis, infections, eczema…etc where as certain changes are said to be allergic in origin. Identifying between the two would be a difficult task as not all diseases or allergic reactions would give a classical picture and in most instances, an underlying cause would not be apparent.

Now let us see, what are the skin manifestations which can crop up either as a disease or else as an allergy and sometimes with both.


Itching is a manifestation that can have many origins and it may be due to a local cause as well as due to an intrinsic cause as well. At the same time, a local irritation can give rise to an itch pertaining to that particular region and intrinsic causes such as liver disease may give rise to a more generalized itch. It may occur as a slight swelling in the region of an allergenic exposure and it may present in the peripheries of a skin would or a cellulites as well. So, the ultimate verdict will be that it can present both with a disease as well as with an allergy but, the frequency of its onset, distribution, other associated factors…etc can give us an idea as to, what is its origin?


Swelling can be a generalized sign in many of the skin related manifestations and more noticeable in an allergy, this would manifest as ‘hives’. These manifestations will crop up suddenly and could be wide spread or localized to a specific region as well. It will be associated with an itch in most cases and will appear as pale red elevations that can crop up in isolation or else as groups. Therefore, hives are manifestations which can be used to differentiate between a skin disease and an allergy.

Other manifestations and the speed

In skin diseases, it is most likely to be present for number of days whereas an allergic reaction would be swift to manifest as well as to resolve. A disease may give rise to tenderness, pus discharge and associated fever…etc whereas a skin allergy may not be linked with such developments. But, in case a person scratching an allergic manifestation in the skin, it may become infected secondarily giving rise to a similar picture.

At the same time, an allergic reaction in the skin, if it is very severe, can be accompanying systemic symptoms such as breathing difficulties, chest tightness, nausea and vomiting as well as move rapidly in developing these symptoms.

Underlying cause

When a person develops a localized skin allergy, it may be possible to find out a possible cause such as wearing a nickel plated wrist watch, working in the garden that afternoon, wearing a garment which he or she may not used to wear, eating certain foods which might give rise to allergic reactions…etc. But, it should be remembered that, this is not the case all the time and the clinician should judge the underlying causative mechanism to the best of their experience and judgment.

As you can see, differentiating between the two is not that easy and proper history, clinical examination and exclusion of other medical conditions through laboratory investigations can give a definite idea as to what you are dealing with in presentations which deviate from a classical allergy manifestation or else from any other disease.