I exercise and eat healthy. are some people just born with really strong immune systems?

Rather weaker system: Great job with eating well and exercising. Some people are born with more compromised immune systems rather than 'stronger'. As a rule, always wash hands well to avoid becoming ill. Continue with your healthy eating habits and regular exercise. Moderation if the key.

Yes,: but eating a healthy diet, getting regular exercise and regular rest are essential for the immune system to function at its best. Stress affects cortisol and immunity too. Also, avoidance of germs by regular handwashing before meals decreases infection as well. Some research supports that exposure to friendly germs as a young child may stimulate immunity opposed to the "too clean" environment.