a brush which includes a straight wand defining a major axis ; a flexible core which defines the length of the brush , the core including a first end and a second end , the first end being secured to the wand . a plurality of bristles are inserted radially into this core , the end of the bristles defining an envelope surface of the brush , the envelope surface having a first end and a second end , wherein the core is curved in a plane of curvature and the envelope surface of the brush over at least part of its length has a cross - section of elongate shape in the direction of an axis of greatest length perpendicular to the plane of curvature .