(And it's not what you think.)
OK, the toddler has a cold; and despite constant hand washing, Vitamin C, disinfectants and independent play, now you have a cold too. The new goal is: Keep the Baby Healthy!!
So you continue to scrub your poor raw hands after every sneeze or used Boogie Wipe (yours or the toddler's). Hand sanitizer is rubbed into every aching pore of those dry, chapped hands each time you pick up the baby. No more snuggling on the couch or kisses on her head. You even breathe in the opposite direction when holding her. You take every precaution the medical industry recommends.
Despite it all, now the baby has a cold. How on earth?!
Then it dawns on you. As per common wisdom, you've been coughing into your elbow, rather than your hand. Your hands have been getting washed every two minutes all day long . . . your elbow hasn't. The same elbow you use to support the baby when you're holding her . . .
. . . Well darn.