Cortisone creams and skin preparations are a large family of drugs all similar to hydrocortisone. The medicines in this family differ primarily by the strength of each compound. 
Hydrocortisone is a natural chemical made by the body and is one of the weakest members of this group. In general steroid ointments are stronger than steroid creams because the medicine penetrates better when in an ointment form. Examples of these medications include: Aristocort, clobetasol, Cortisone 5 & 10, Diprolene, Elocon, fluocinolone, Halog, hydrocortisone, Hytone, Lidex, Psorcon, Temovate, triamcinolone, Ultravate, and Valisone. There are many other examples.
What do cortisone creams do?
These treatments can decrease local inflammation, swelling, burning, and itching. In ointment form, they can help the skin maintain moisture. Cortisone can help with many different skin conditions from poison ivy/oak to allergic dermatitis as well as eczema, insect bites and rashes.
Are there any side effects to worry about?
Strong cortisone ointments and creams may cause permanent thinning of the skin, especially when applied to skin-folds such as under the breast, the armpit, and the groin. Strong preparations should also be avoided on the face and the fingertips. The risk of permanent thinning of the skin is increased when plastic wraps (Saran wrap) are used. Daily application of alpha hydroxyacids can help to lessen this side effect.
Sometimes cortisones can cause an acne-like rash when applied to the skin. Weak cortisones can be used on small areas of the body for years without causing permanent side effects.
Safety concerns and proper usage
Cortisone skin preparations are generally regarded as safe. They can even be bought in low strength forms without a prescription. The following situations can lead to enough internal absorption through the skin to cause side effects:
Always use small amounts of cortisone creams and massage gently into your skin. A little bit should go a long way. Excess cortisone left on the skin is wasted. Keep this medicine out of the eyes and mouth.
Sometimes the doctor will have you alternate two different cortisones ointments or creams. This helps cut down on the resistance which develops to the use of cortisone ointments and creams when the same one is used everyday.
You should skip using the medication a couple of days each week. This decreases the chances of developing side effects.
There are many chronic skin conditions which have no cure that require the continued use of topical cortisone medication. If you have such a condition you need to minimize as much as possible the use of these types of medication by skipping days when the condition is under good control. On these days just use plain Vaseline or Aquaphor available from your pharmacy without a prescription.