The NHS forks out more than £16 million a year on bath emollients, equivalent to almost 40% of the total cost of eczema treatments prescribed for pre-school children, says DTB.
There is little published research on the benefits of the gels, creams and lotions applied to ease the symptoms of various dry skin conditions, including eczema, as a whole, says DTB.
But there is no evidence to show that bath products, most of which contain liquid paraffin, work. And even the medical experts can't agree on their effectiveness, it says.
Emollients are used to improve the symptoms and appearance of dry skin conditions and cut down on the use of steroid creams.
The theory behind their use is that they prevent water loss from the skin and form a protective barrier against external skin irritants.
The long experience of healthcare professionals indicates that normal emollients applied directly to the skin are effective, says DTB.
There is some published research to back this up. And national treatment guidelines widely recommend the liberal use of emollients two to three times a day, including after bathing.
But there is no such consensus for bath emollients, says DTB.
And important questions, such as how these products compare with other bathing products and the use of skin creams after washing, have not been answered.
Yet healthcare professionals frequently tell patients to use them, and the British Association of Dermatologists also recommends their use in its advice to patients.
"Given that bath emollients are expensive, and the NHS spends a considerable sum on them, we believe their use requires proper evaluation," says DTB.
And adequate application of topical skin creams without the addition of bath emollients is "entirely reasonable," it concludes.