Rash

Red, itchy bumps or patches all over the place

Outbreaks of this sort are usually either viral or allergic.
Viral rash: While viral infections of the skin itself, like herpes or shingles (a cousin of chickenpox), are mostly localized to one part of the body, viral rashes are more often symmetrical and everywhere. Patients with such rashes may or may not have other viral symptoms like coughing, sneezing, or stomach upset (nausea). Viral rashes usually last a few days to a week and go way on their own. Treatment is directed at relief of itch, if there is any.
Allergic drug rash: Most allergic drug rashes start within two or three weeks of taking a new medication, especially if the person has taken the drug before. It is very unlikely for medicine that has been prescribed for months or years to cause an allergic reaction. Because there is usually no specific test to prove whether a rash is allergic, doctors may recommend stopping a suspected drug to see what happens. If the rash doesn't disappear within a week of not taking the medication, allergy is unlikely.
Although foods, soaps, and detergents are often blamed for widespread rashes, they are rarely the culprits.
Other rashes
Hives (urticaria) are itchy, red welts that come and go on various parts of the body. Most hives are not allergic, run their course, and disappear as mysteriously as they came. Heat rash is a skin irritation caused by excessive sweating during hot, humid weather. It can occur at any age but is most common in young children. Heat rash looks like a red cluster of pimples or small blisters. It is more likely to occur on the neck and upper chest, in the groin, under the breasts, and in elbow creases.

What is the treatment for a rash?

Most rashes are not dangerous to a person or people in the vicinity (unless they are part of an infectious disease such as chickenpox). Many rashes last a while and get better on their own. It is therefore not unreasonable to treat symptoms like itchy and/or dry skin for a few days to see whether the condition gets milder and goes away.
Nonprescription (over-the-counter) remedies include

• anti-itch creams containing camphor, menthol, pramoxine (Itch-X, Sarna Sensitive), or diphenhydramine (Benadryl);
• antihistamines like diphenhydramine (Benadryl), chlorpheniramine (Chlor-Trimeton), or loratadine (Claritin, Claritin RediTabs, Alavert); and cetirizine (Zyrtec);
• moisturizing lotions.

If these measures do not help, or if the rash persists or becomes more widespread, a visit to a general physician or dermatologist is advisable.
There are many, many other types of rashes that we have not covered in this article. So, it is doubly important, if you have any questions about the cause or treatment of a rash, to contact your doctor. This article is really just as the title indicates: "Rash 101: Introduction to Common Skin Rashes."
A word on smallpox vaccination in patients with rashes
People with atopic dermatitis or eczema should not be vaccinated against smallpox, whether or not the condition is active. Patients with atopic dermatitis are more susceptible to having the virus spread on their skin, which can lead to a serious, even life-threatening condition called eczema vaccinatum. In the case of other rashes, the risk of complications is much less. Consult your doctor about the smallpox vaccine.