Final answer:
Recent research suggests that exposing children to allergenic substances during infancy might help prevent some allergies, in line with the hygiene hypothesis, but must be approached with medical guidance.
Step-by-step explanation:
The best time to potentially expose a child to an allergic substance has been a subject of much debate and research. While traditionally, it was thought that such substances should be avoided entirely to prevent allergies, more recent evidence suggests that early introduction of certain allergenic foods during infancy could help prevent some food allergies. This is closely related to the "hygiene hypothesis," which implies that limited exposure to microbes and certain allergens in early childhood can lead to an increase in immune system-related problems. However, it is important to approach this matter cautiously and usually under the guidance of a healthcare professional, as each child's health circumstances are unique.