The Fallout Shelter FAQ, Section 4: Dweller Happiness and Health

https://github.com/therabidsquirel/The-Fallout-Shelter-FAQ/wiki/Section-4:-Dweller-Happiness-and-Health

Community FAQ. Happiness stabilizes at 50%, or 75% in a room matching the dweller's highest SPECIAL stat; successful and failed rushes shift it by 10%; breeding raises both parents to 100%; radio rooms nudge vault-wide happiness; heavy injury and radiation lower it, and enough food and water avoids both; health gained at level-up depends on Endurance at that moment.

Fallout Shelter