Itching and rashes may develop as the result of infection or irritation, or from a reaction of the immune system. Some rashes occur mostly in children whereas others almost always occur in adults. Sometimes an immune reaction is triggered by substances a person touches or eats. The diagnosis of most noninfectious skin rashes is based on the appearance of the rash. The cause of a rash cannot be determined by blood tests, and tests of any kind are rarely performed. However, persistent rashes may lead the doctor to perform a skin biopsy, or if the doctor suspects a contact allergy as the cause skin tests may be performed

 

Contact dermatitis is an inflammation of the skin caused by direct contact with an irritant or allergen. Irritant dermatitis, the most common type of contact dermatitis, involves inflammation resulting from contact with acids, alkaline materials such as soaps and detergents, solvents, or other chemicals. The reaction usually resembles a burn.
Allergic contact dermatitis, the second most common type of contact dermatitis, is caused by exposure to a substance or material to which you have become extra sensitive or allergic. The allergic reaction is often delayed, with the rash appearning 24-48 hours after exposure. The skin inflammation varies from mild irritation and redness to open sores, depending on the type of irritant, the body part affected, and your sensitivity.
Sometimes it is easy to recognise irritant contact dermatitis and no specific tests are necessary. The rash usually heals once the irritant is removed and, if necessary, special treatment is applied. While there are some tests that can provide an indication of the irritant potential of substances, there are no specific tests that can reliably show what the effect of an irritant will be in each individual case. Irritant dermatitis in any case is usually the result of the cumulative effect of multiple irritants. Patch tests may be used to confirm allergic contact dermatitis and identify the allergen(s), but they do not exclude irritant contact dermatitis as the two may coexist.
Though the configuration of the rash aids in diagnosis, it's not so easy to determine whether an allergy or irritant is involved. The skin reaction produced by either, especially when mild, frequently looks the same. Redness or an itchy rash may be the first sign: however, blisters that weep or form a crust, along with swelling, are more likely to appear in allergic dermatitis such as poison ivy. As the inflammation lessens, the skin may scale and become temporarily thickened. When the dermatitis becomes chronic, the skin becomes dry, thickened and cracking. If the inflammation mild irritants continues for a long time, the original irritation disappears because the skin becomes hardened.
 
Atopic Dermatitis, often call eczema, is a common, often chronic skin disease that affects a large percentage of the world's population. It is also called eczema, dermatitis, or atopy: the atopic dermatitis triad includes asthma and allergies (hay fever). Most commonly, it may be thought of as a type of skin allergy or sensitivity. The hallmarks of the disease include skin rashes and itching.
Atopic dermatitis can occur at any age, but it often affects infants and young children. In some instances it may persist into adulthood. In most cases there are periods of time when the disease is worse, followed by remissions when the skin improves or clears up entirely. Many children with atopic dermatitis enter into a permanent remission of the disease when they get older although their skin may remain dry and easily irritated.
Multiple factors can trigger or worsen atopic dermatitis including dry skin, seasonal allergies, exposure to harsh soaps and detergents, new skin products or creams, and cold weather. Environmental factors can also activate symptoms in individuals who have inherited the atopic disease trait.
Although symptoms of atopic dermatitis can be very difficult and uncomfortable, the disease can be successfully managed. People with atopic dermatitis can lead healthy, normal lives. Long-term management may include treatment with an allergist to control internal allergies and a dermatologist to monitor the skin-care component.
 
Dyshidrotic Dermatitis is a skin condition characterized by small blisters on the hands or feet. Recurrence is common and for many can be chronic. This condition is not contagious to others, but due to its unsightly nature can cause significant distress in regards to social interaction.
Dishydrotic eczema can have a host of causes, some obvious allergens and others not so much. Obvious allergens like animal dander, soaps, laundry detergents and perfumes. It can also be triggered by some not so obvious substances such as food, chemicals and even some metals like that in costume jewelry. Foods that can cause eczema include strawberries, nuts, seafood, eggs and wheat. Emotional stress can make dyshidrotic dermatitis worse, but does not cause it. Ingestion of allergens such as chromate, neomycin, quinoline, or nickel may cause some cases. Many people with atopic dermatitis also have dyshidrotic dermatitis, which may mean that dyshidrotic dermatitis is just a form of atopic dermatitis on the hands and feet.
As there is no actual cure available for dishydrotic eczema, the main aim is to treat it in order to reduce the discomfort and the inflammation caused and slow down the rate of cell division. There are many treatments available such as steroid creams, ointments, cortisone, etc, but they should be taken only under a doctor's prescription. If the infection is caused due to bacteria then there are antibiotics and prescribed drugs that will help to prevent itching.