Chapter 16: The Skin

RULES FOR PRESCRIBING CREAMS AND OINTMENTS

How much cream?

On average, 30 g of cream will cover the body surface area of an adult. Ointments, despite being of a thicker consistency, do not penetrate into the deeper skin layers so readily, and the requirements are slightly less. Pastes are applied thickly, and the requirements are at least 3 to 4 times as great as for creams.

The ‘rule of nines’, used routinely to determine the percentage of body surface area affected by burns (Fig. 16.1), may be used also to calculate the amount of a topical preparation that needs to be prescribed.

For example:

• If 9% of the body surface area is affected by eczema, approximately 3 g of cream is required to cover it.

• Nine grams of cream is used per day if prescribed 3 times daily.

• A 50 g tube will last 5 or 6 days.

One gram of cream will cover an area approximately 10 cm × 10 cm, and this formula may be used for smaller lesions.

Some general rules

1. Use creams or lotions for acute rashes.

2. Use ointments for chronic scaling rashes.

3. A thin smear only is necessary.

4. On average, 30 g:

   • will cover an adult body once

   • will cover hands twice daily for 2 weeks

   • will cover a patchy rash twice daily for 1 week.

5. On average, 200 g will cover a quite severe rash twice daily for 2 weeks.

TOPICAL CORTICOSTEROIDS FOR SUNBURN

When a patient with severe sunburn presents early, the application of 1% hydrocortisone ointment or cream can reduce significantly the eventual severity of the burn. This has been proved experimentally by covering one-half of the burnt area with hydrocortisone and comparing the outcome with the untreated area.

The application can be repeated 2 to 3 hours after the initial application and then the next morning. The earlier the treatment is applied the better, as it may not be useful after 24 hours.

Hydrocortisone should be used for unblistered erythematous skin, and not used on broken skin.

SKIN EXPOSURE TO THE SUN

There is evidence that our skin needs exposure to sunlight to provide a substantial dose of vitamin D. This is a preventive for osteoporosis. Hats and sunscreens prevent the natural synthesis of vitamin D in the body.

There should be a balance between receiving enough sunlight exposure to prevent vitamin D deficiency on one hand and receiving too much, predisposing to skin cancer, on the other (see Table 16.1). A simpler guideline for most geographical areas is to recommend ...