A substance which is normally harmless that provokes an immune response and thus and allergic reaction. While some people have no reaction to pollen, others may have an allergic reaction. The same is true for a wide range of scents, odors, foods and natural substances.
Daily Hair Tip
Whenever possible limit or avoid using a brush on curly tresses. Instead use a widetooth pick or comb with "hair friendly" edges that won't rip or tear fragile curls.