How do you avoid it with lead solder? Common soldering tutorials don't mention the issue.
Common rules are: Work in a well-ventilated area, don't eat while working, don't use your soldering iron to heat your coffee. But those apply while using lead-free solder as well.
edit: so, it's the frequent repeated exposure to lead (i.e. in paint and as a sugar added to wine[0]) which is harmful, not any single individual (non-acute) exposure.
[0]: https://en.wikipedia.org/wiki/Lead(II)_acetate#Sweetener
itching
vertigo
dizziness
tingling in extremities
loss of balance or coordination
slurred speech
temporary blindness
profuse sweating
or heart palpitations.
If lead-based solder begins to smoke, get away immediately. Seek shelter and cover head. Lead-based solder may stick to certain types of skin. When not in use, lead-based solder should be returned to its special container and kept under refrigeration. Failure to do so relieves the makers of lead-based solder, Wacky Products Incorporated, and its parent company, Global Chemical Unlimited, of any and all liability. Ingredients of lead-based solder include an unknown glowing green substance which fell to Earth, presumably from outer space. Lead-based solder has been shipped to our troops in Saudi Arabia and is being dropped by our warplanes on Iraq. Do not taunt lead-based solder. Lead-based solder comes with a lifetime warranty.