Allergic contact dermatitis occurs when your skin comes in contact with an allergen that your skin is sensitive or allergic to. The reaction usually appears within 48 hours after the initial exposure to the allergen. 
Symptoms that are commonly seen include the following: redness, swelling, blistering, itching, and weeping.
The allergen can be a substance in a product that you have used for many years; it does not have to be a new product that you are exposed to. It occurs more commonly in adults, but can be found in adolescents as well. The most common types of allergic contact dermatitis are allergy to poison ivy and poison oak.
What causes allergic contact dermatitis?
Whether or not you are allergic to something is determined by your genes. Many people believe that you cannot be allergic to a product that you have used everyday for many years, but this is not the case. At any time your skin can become allergic to one of the specific substances in the product, even if you have used it for a long time.
Oftentimes, a rash may break out on your face even if you did not come in direct contact with the allergen. If you get something on your hands that you are allergic to and then touch your face, the allergen can cause a reaction on the face even though there is no reaction on your hands. This is because the skin on our hands is thicker than that of the face, especially around the eyelids.
What are the best treatments?
For starters, you have to discontinue all products that you have been using on the exposed area, and only use the treatment a dermatologist has prescribed for you. The most common treatment for allergic contact dermatitis is a cortisone ointment preparation.
Many people opt for the more effective natural treatments such as Puriya Cream, which can stop the itching and minimize the redness.
If you do opt for the cortisone, it is important that you return to your dermatologist at the end of your one to two week treatment. The treatment used is strong and you should not use it for more than one to two weeks without being under the supervision of your doctor. If overused, the medication can cause permanent thinning of the skin. When you come for the second visit, if all is going well, your doctor will then taper down to a weaker medication.
Two weeks after your symptoms have cleared, you can begin the search for the chemical that you are allergic to. You do this by re-introducing the products you were using prior to your reaction, one at a time, one week apart. It is often best to do a small test area first.
If you have a good idea what you are allergic to, you can simply try to avoid it in the future and you should not have any further problems. If your problem persists however and you are unable to determine the cause, patch testing may have to be done. This will be explained in greater detail if it is required.
In any case, rest assured that contact dermatitis is extremely common, and everyone has an allergic reaction to one thing or another at some point in their lives. Just try to be aware of what it is that is causing the breakout, and try your best to not come into contact with it going forward.