Rickets is a disease that affects growing bones, making them soft and weak instead of hard and strong. Children with rickets might develop bowed legs, a curved spine, or bones that break easily because their bodies aren't getting enough vitamin D, calcium, or phosphorus to build healthy bone tissue.

Think of bones like concrete: they need the right ingredients to harden properly. Vitamin D helps the body absorb calcium from food, and calcium is what makes bones solid. Without enough vitamin D, bones stay soft and bendy, like rubber instead of stone. A child's legs might bow outward under their body weight, or their wrists and ankles might swell.

Rickets was common in crowded industrial cities during the 1800s and early 1900s, where children rarely saw sunlight (which helps the body make vitamin D). Today it's rare in developed countries because milk is fortified with vitamin D and most children get adequate nutrition and sunshine. The disease is preventable and treatable: getting enough vitamin D through diet, supplements, or safe sunlight exposure helps bones grow strong and straight.

You might also encounter the adjective rickety, which describes something wobbly or poorly constructed, like a rickety old chair that wobbles when you sit on it.