The drive will support ads, by Grey, that break in May.
The account was previously held by Euro RSCG Biss Lancaster, which won the brief four years ago (PRWeek, 15 Feb 2002) and ceased to work on it last year.
C&W has a five-strong team, led by associate director Pat Hindley, on the brief. She reports to Piriton brand manager Helly Seeley.
Hindley said: 'Over the next few months we hope to show a new generation of allergy sufferers how they can best relieve their symptoms.'
C&W already works for GSK in consumer health, promoting its smoking-cessation brand NiQuitin CQ.