There was a time when the air on airplanes was truly awful, but the days of smoking in flight are long gone. I know I am dating myself, but I remember passing out five-packs of cigarettes to passengers in first class; the flight attendants kept the leftovers for themselves. That was when smoking was considered sophisticated, and no one thought very hard about what was happening to their lungs.

Times changed, and smoking was relegated to the back of the airplane. But it was ridiculous to call 39A a nonsmoking seat when 40A was the start of the smoking section. The smoke would drift forward and enter the air system; by the end of the flight, everyone smelled like a cigarette butt. Soon smoking was sent packing.

You would think that with the departure of tobacco we all would be breathing a lot easier. But not so — at least according to some travelers. Many people believe that recirculated cabin air deprives passengers of oxygen, spreads disease and dries people out like prunes. Others believe that low oxygen levels on airplanes often cause hypoxia; affected passengers, they say, just don’t recognize the symptoms. Of course, the airlines periodically conduct their own “scientific” studies, which uniformly conclude that cabin air is perfectly healthy.

Who’s right? Let’s consider a few common myths.

Myth: Pilots recycle the air and deprive the cabin of fresh oxygen in order to save fuel.

Fact: Well, yes and no. On newer airplanes, fans recirculate 50 percent of the cabin air, but fresh air is continuously pumped in from outside. Pilots do have the ability to turn off the fans and pump in only fresh air, but this is not standard operating procedure because it would consume too much fuel. Fresh air would improve the air quality in the cabin somewhat, but it would not raise the oxygen level.

Myth: The cabin air is drier now than it used to be.

Fact: Actually, the air is probably moister, but you’re not going to like the reason. The recirculation of the cabin air raises the humidity level by taking up passengers’ breath exhalations, sweat, sneezes and other bodily effluvia. But I prefer not to think about that too much.

Myth: The cockpit has five times more oxygen than the cabin.

Fact: No. The oxygen level is the same throughout the plane at all times. The flight deck does receive a higher proportion of colder, outside air than the rest of the cabin; this is to compensate for the heat generated by the electronic equipment in the cockpit. Remember, oxygen level and air quality do not go hand in hand. The higher concentration of fresh air in the cockpit may make for a fresher environment for the pilots, but the oxygen level is no different from what you get in first class or coach.

Myth: The airline never cleans the air filters and this spreads disease.

Fact: Actually, the air is quite healthy because of the High Efficiency Particulate Air (HEPA) filters, which can catch up to 99.9 percent of small bacteria and viruses (even SARS and bird flu virus). The filters actually become more effective over time as trapped particles make it even more difficult for other matter to pass through. Nevertheless, the filters are replaced on a regular schedule; otherwise, a large buildup would reduce the flow of oxygen and cost the airline money. So, if you come down with a cold after a flight, don’t blame the filters. Blame your sneezy seat neighbor.

Myth: The air quality is better in first class and worse in the back of economy.

Fact: This is actually true, and it is due to the design of the airplane. Oxygen comes in from the front of the airplane and exits out the rear in a system called FART (Forward Air, Return Tail). Quite ironic, but I won’t go any further with that one.

Now, having said all of that, there are things to look out for and precautions to take to make sure the cabin air remains healthy and to keep the germs away.

1. Count headaches. If an unusually high number of your seat neighbors complain about headaches or dizziness, contact a flight attendant. Ask if others have the same symptoms, and if so, ask that the cockpit turn off the recirculation fans for a while. This won’t increase the oxygen level, but it will improve the air quality.

2. Turn on the vent. In my experience, most people who complain about stale air do not have their vent turned on. You would be surprised what a little direct air can do for the mind and body.

3. Wash up. If you are afraid of catching a cold from your seat neighbor, make sure you wash your hands every chance you get and avoid touching your face. Better yet, bring antibacterial hand wipes along with you.

4. Get ionized. The new trend is to wear a small personal air ionizer around your neck. The device purportedly sends a stream of air-purifying ions up toward the nose. You might get some stares, but some people swear by these things.

5. Hit the bottle. If you are suffering from headache, nausea, confusion or clammy skin, or if you are having difficulty breathing, ask a flight attendant for supplemental oxygen. Airlines are required to carry it and to dispense it at no charge.

6. Bug out. Some destinations require airline personnel to spray insecticide before landing. This is not an airline requirement but the destination’s requirement, so don’t get mad at the flight attendants. Instead, wet a handkerchief, or if you are well prepared, don a disposable surgical mask before they spray.

7. Squelch the sneezers. If someone is sneezing or coughing and not covering his mouth, don’t be afraid to say something. Once I was flying standby and was afraid to speak up about a cougher. I ended the flight with a hair full of phlegm and a weeklong cold.

8. Don’t obsess. There is a businesswoman who is often on my flights. She is in her late 50s, always conservatively dressed and very polite. Right before takeoff, she always puts on an elaborate hat made completely of aluminum foil. She doesn’t laugh or make light of it; she believes the hat protects her from solar radiation. But, really, you don’t need such a hat, and you shouldn’t obsess about the air quality on the plane, either. Your stay on the airplane is brief, and the air you breathe is no more dangerous than the air in your workplace.

But people still have their worries, and commerce has bravely stepped forward to meet them, offering such products as special facemasks and personal filters that fit over the air vent above your seat. I have even seen oxygen bars at some airports. If I know the airline industry, it is busy concocting some way to charge you for the oxygen, too.

If only the airlines would start using some common sense. Now, that would be a breath of fresh air.