You encounter billions (!) of germs when you travel.

Every surface from tray tables to taxi seats to hotel doors is teeming with germs.

Infectious airborne particles can easily spread from person to person in close quarters. Planes pose particularly unique risks.

Here are some common bacteria and viruses that show up in surface and air samples at airports and on planes:
pseudomonas, stenotrophomonas, staphylococcus, E. coli, klebsiella, acinetobachter, propionibacteriaceae, and streptococcaceae, rhinovirus, and influenza virus.

Travel can be stressful, especially business travel. Stress weakens immune function.

Dehydration is common when traveling, especially when flying.

At just 10-20% humidity, an airplane cabin is drier than the Sahara desert! For every hour of flying, you lose 8 ounces of water. This leaves most people incredibly dehydrated.

At low humidity, skin and mucous membranes dry out, and flu viruses are both easier to catch and last longer.

Most people also forget to drink enough water when they're away from home.

If you've ever felt fatigued while traveling, there are many reasons for that.

While flying, you take in less oxygen due to the cabin pressure.

When traveling in vehicles, the constant sways, jerks, and jumps are taxing on the brain and muscles.

When traveling in general, you're also on higher alert of your surroundings which adds to mental exhaustion.

The fluctuating pressure, oxygen, and temperature in planes causes your stomach and intestines to expand.

Your body also has to work harder to circulate blood to the limbs in the face of high altitude and dry air, leading to digestive issues such as gas and bloating.

Sitting for extended periods of time in planes and cars slows blood flow through the arms and legs, increasing the risk of serious issues like blood clots.

If you cross time zones, your circadian rhythm is disrupted, impacting your sleep, energy levels, focus, and mood.

Air travel exposes you to radiation because at high altitude, the air is thinner. Thinner air means fewer molecules to deflect incoming cosmic rays (radiation from outer space).

While the radiation dose rate at commercial airline flight altitude is ~0.003 mSV per hour (a very low dose), for regular travelers who fly tens of thousands of miles every year, that cumulative radiation exposure increases the risk of cancer later in life.

Healthy diet, exercise, and sleep routines you've developed are harder to maintain when away from home.