Several formulations are available for topical steroids, intended to suit the type of skin lesion and its location.   

A topical steroid is applied once daily (usually at night) to inflamed skin for a course of five days to several weeks. After that, it is usually stopped, or the strength or frequency of application is reduced. Emollients can be applied before or after the application of topical steroid, to relieve irritation and dryness or as a barrier preparation. Infection may need additional treatment. Creams and lotions are general purpose and are the most popular formulations. Ointments are most suitable formulation for dry, non-hairy skin.   

They don’t contain preservatives, reducing risk of irritancy and contact allergy. However, they are occlusive, increasing risk of folliculitis and miliaria. Gels or solutions are useful in hair-bearing skin. They have an astringent (drying) effect and can cause stinging on inflamed skin.  

FINGERTIP UNIT 

The fingertip unit guides the amount of topical steroid to be applied to a body site. One unit describes the amount of cream squeezed out of its tube onto the volar aspect of the terminal phalanx of the index finger.  

The quantity of cream in a fingertip unit varies with sex, age and body part. 

• Adult male: one fingertip unit provides 0.5g
• Adult female: one fingertip unit provides 0.4g
• Child aged four years: approximately 1/3 of the adult amount
• Infant six months to one year: approximately 1/4 of the adult amount
• One hand: apply one fingertip unit.

 Amounts to use: 

• One arm: apply three fingertip units
• One foot: apply two fingertip units
• One leg: apply six fingertip units
• Face and neck: apply 2.5 fingertip units
• Trunk, front and back: 14 fingertip units
• Entire body: about 40 units.

The choice of topical steroid will depend on the person’s age, how severe the eczema is, and which area of the body is affected.  Low-potency and moderate-potency corticosteroids are usually enough to keep eczema at bay. Generally speaking: 

Topical corticosteroids of low to moderate potency are particularly suitable for the treatment of eczema in areas where the skin is sensitive and thin. These include the face, the back of the knees, the insides of the elbows, the groin area and the armpits

• High-potency and ultra-high-potency corticosteroids are used for the treatment of severe eczema on the palms of the hands and soles of the feet, or for the treatment of eczema on very thick skin
• High-potency and ultra-high-potency corticosteroids shouldn’t be used on rashes that cover a large area of skin
• Very sensitive areas such as the neck or genitals should only be treated with low-potency corticosteroids.

It is also possible to switch between products of different strengths. For example, some doctors recommend starting treatment with a high-potency corticosteroid to get the flare-up under control as quickly as possible, and then switching to a weaker corticosteroid after a few days. Others prefer to start with a low-potency corticosteroid and only change to a stronger one if the first medication doesn’t work well enough. It’s best to talk to the doctor about the preferred strategy.   

Sources: NHS, DermNet, NIH