Leaded solder has been being used for decades now. It offers smooth, silver bright (in color) finishing. Its preferred due to the ease it offers when soldering: a lower melting point and a good looking finishing. However, Its numerous health effects fuels user’s demand to rule it out.
Lead is used in the soldering process in the form of lead/silver filler metals. When heated, lead oxide fumes are formed. Excessive exposure to lead oxide fumes can result in lead poisoning. Lead is absorbed through the mucous membranes of the lung, stomach (Don’t eat while soldering), or intestines and then enters the bloodstream. Worse, lead absorption is cumulative as it is slow to leave the body.
Symptoms include loss of appetite, indigestion, nausea, vomiting, constipation, headache, abdominal cramps, nervousness, and insomnia. Lead is absorbed through the mucous membranes of the lung, stomach, or intestines and then enters the bloodstream".
On the extreme, absorption of lead is known to cause birth defects, cancer and other reproductive harm and may result for example in damage to the blood and neurological systems.
Ventilation is probably the most important engineering control available to the safety and health professional to maintain airborne concentrations of lead at acceptable levels. It is advised to solder only with adequate ventilation and respiratory protection when necessary. You should get suitable ventilation equipment and ensure that the fumes are sucked outside. In other words, the traditional soldering with a fan blowing the fumes away from your face but circulating it within the room is primitive and useless. You'll need a dedicated ventilation system.
Wash thoroughly before eating, drinking or smoking. There is danger from using lead solder and getting it on your hands and then eating. So don't eat while soldering.