I recently experienced an itchy rash all over my body. I am not sure what it is. Does this mean that I am having an allergic reaction?

Not all itchy rashes are allergic reactions, although many of them are.

Basically, there are many types of allergic reactions. They look different and are called by different names, so people are confused by them.

Allergic skin conditions are skin conditions that are caused by an allergen (usually a foreign entity to the body but can involve our own body components) that trigger an immune response.

This immune response then manifests in our bodies and skins. The latter is called an allergic skin reaction.

Allergic skin conditions can be difficult to identify, especially if you are a non-medical person. And even many general practitioners and doctors have difficulty identifying them, leading to a lot of wrong diagnoses.

It usually takes a dermatologist to identify them properly.

They can be divided into hives and angioedema as well as dermatitis, which also be divided into eczema or contact dermatitis.

The medical term for hives is urticaria. They are red, raised, and itchy areas on your skin.

These areas differ in size and can appear anywhere on your body. They are usually acute – appearing suddenly – and will disappear within a few days or weeks.

Some people have chronic hives, however, which can go on for many months, or even years.

There is usually an allergen, or substance that triggers these hives, especially for acute cases.

Sometimes, it is very difficult to identify the trigger. A lot of times, you find the trigger based on trial and error.

For example, if you eat a certain type of biscuit, you notice that the hives come on. On further trial, you discover that the ingredient that you are allergic to is sesame.

You can then avoid eating sesame in the future.

Blood testing and allergy screens are not usually effective in identifying the trigger.

The treatment remains the same – antihistamines. It should be noted that in many chronic cases, there is no allergic cause found.

Angioedema is swelling that involves the deeper layers of your skin. It is not red or itchy. It often involves the eyelids, lips, tongue, hands and feet. It usually occurs with hives, but can occur on its own.

Naturally, it’s more alarming and serious than hives, and usually sends people who are affected running to the doctor, and sometimes to the emergency room.

Common triggers of hives and angioedema include foods, bee or insect stings, some drugs, certain viruses or bacteria. Sometimes, even heat or cold, the sun, exercise and pressure can induce hives.

Dermatitis is an inflammation of the skin. The rash here is red, scaly and itchy.

There are two types.

Eczema, also known as atopic dermatitis, is an irritating and very life-altering condition which can differ in severity. It usually begins in childhood or even infancy.

It is associated with other allergic diseases such as asthma and allergic rhinitis.

Contact dermatitis occurs when certain substances come in contact with your skin.

Irritant contact dermatitis happens when a substance damages the part of skin it comes in contact with. It is often more painful than itchy, and usually occurs on your hands or whatever area of your body that comes in contact with the substance.

For example, if you are allergic to bleach and you don’t wear gloves when using bleach to mop the floor, your hands may experience this type of dermatitis.

Allergic contact dermatitis is the other type. When you touch something, it not only causes an allergic reaction in the area of skin in direct contact, but also in other parts of your body.

For example, this can occur when you touch poison ivy or certain chemicals and dyes.

The itching in eczema can be severe and is especially bad at night.

Eczema appears as brownish red patches, and especially affects the hands, feet, ankles, wrists, the inside of elbows and knees, neck and upper chest.

The skin in these areas can be dry and scaly. It gradually becomes thickened and cracked in chronic cases.

Dr YLM graduated as a medical doctor, and has been writing for many years on various subjects such as medicine, health, computers and entertainment. For further information, e-mail starhealth@thestar.com.my. The information contained in this column is for general educational purposes only. Neither The Star nor the author gives any warranty on accuracy, completeness, functionality, usefulness or other assurances as to such information. The Star and the author disclaim all responsibility for any losses, damage to property or personal injury suffered directly or indirectly from reliance on such information.