Potential Health Problems


graphic via the FDA
graphic via the FDA

The Pacific Crest Trail is not the long green tunnel of the AT but the spectacular daily vistas come with a price: full sun exposure nearly every day. There is little shade in the first 700 miles of desert or above treeline and once in the Sierras, the high altitude means more intense solar radiation.

For these reasons we recommend wearing long sleeve shirts and pants, wide-brimmed hats, and applying SPF 50 sunscreen to your nose and cheeks. If you have already suffered from skin cancer or melanoma, you will need to be extra cautious during your thru-hike.


In 2012 the FDA revised rules for the labeling and marketing of sunscreens, and announced that the effectiveness of sunscreen plateaus at SPF 50. Higher SPF numbers do not provide more protection, so don't waste your money. We also recommend avoiding anything lower than SPF 50 so that you get the most bang for the extra pack weight.

Glacier Glove All Lycra Sun Glove
Glacier Glove All Lycra Sun Glove

Sun Gloves

Despite wearing long sleeves and big hats, many hikers nevertheless get sunburned on their hands. Sun gloves are thin, light-colored gloves with no insulation. They are worn simply to block sunlight and prevent sunburn. They are almost always sold fingerless. We recommend them. 

Cold Sores & Chapped Lips

Your lips can become sunburnt and windburnt just as easily as your skin, and prolonged exposure to UV light can trigger the virus that causes cold sores. Mountaineers wear high SPF limp balm since UV radiation is stronger at high altitude than at sea level. PCT thru-hikers should do the same while in the Sierras. 


Classic cherry ChapStick has little SPF protection, so look for lip balms that explicitly state their SPF rating. Examples include ChapStick's Sun Defense line and Banana Boat Sport Performance Sunscreen Lip Balm.


Lip balm is also important since the incredible aridity of the western United States causes chapped lips. Even if you are from the West and feel used to the dry conditions, you probably do not spend 12 hours a day outside in the sun and wind. Everyone needs lip balm. 

Severe Dry Eye

Threat of severe dry eye confronts anyone who spends a lot of time outdoors: construction workers, landscapers, paddlers, hikers, et cetera. The combination of wind and aridity on the PCT make the threat particularly bad for hikers.


It can be quite painful and the key is prevention. First, have lubricant  eye drops and use them often, before redness and irritation appear. Lubricant drops can be used while wearing contacts. Do not use Visine or similar products that contains vasoconstrictors. These constrict blood flow to the eyes and cause “rebound redness.” In other words, Visine makes the problem worse. Instead, choose brands like Refresh or Systane.


Second, always wear sunglasses that block 100% of UVA & UVB rays. (Polarized lenses are nice, but they make it difficult to read LCD screens. If you plan to take lots of pictures avoid polarized lenses.)


graphic via urinecolors.com
graphic via urinecolors.com

While completely preventable, dehydration happens anyway, usually because of laziness or impatience.


Filtering water takes time. Stopping to get water means getting to camp late. You want to keep going, to get the miles in, so you ration what you've got and don't drink as much as you should. You tell yourself you're fine and that you'll filter water in camp. You cameled-up before leaving camp that morning. It's not that hot. You're used to the heat. Just three more miles and then you'll stop for lunch. You'll get water then.


We've all been there. Fight these inclinations. Your urine should be copious and clear. If not, you aren't drinking enough water.


It's Common on the First Day

Our evidence is admittedly anecdotal, but it seems many northbound PCT hikers become dehydrated on the first day. In fact, it's possible that the majority of PCT hikers who become dehydrated at some point during their thru-hike get dehydrated on the first day. This is because the first day is tough — from the southern terminus it's 21 miles to the first water source. Hiking the entire 21 miles on their first day is not possible for many hikers (one reason why we recommend training before starting). Additionally, many people are unprepared for how hot temperatures become midday, and do not carry enough water. To prevent dehydration, we recommend leaving the southern terminus with at least 8 liters (2 gallons) per person. 

Hyperthermia / Heat Stroke

Hyperthermia, or the overheating of your body, advances in stages:

   1) heat cramps

   2) heat exhaustion

   3) heat stroke.


The final stage, heat stroke, will be fatal if it happens to someone on the PCT. The danger of heat stroke when in remote, rural areas cannot be overstated, so let's explore the progression of heat illness to understand how to prevent it.


1) Heat Cramps

We have all experienced heat cramps. We've all overexerted ourselves in high temperatures when playing sports, working in the yard, chasing our kids around, kayaking, or backpacking and felt the symptoms:

   1)  lots of sweating

   2)  thirst  (once you feel thirsty, you are already dehydrated)

   3)  lightheadedness

   4)  fatigue

   5)  cramps in the stomach, arms, or legs.


Treatment of heat cramps is common sense: stop what you are doing, get out of the sun, sit down and rest, and drink lots of water or Gatorade (but never beer). Trouble begins when we ignore the signs of heat cramps and push ourselves to keep going.

2) Heat Exhaustion

We bring heat exhaustion on ourselves when we do stupid things like:

   1)  assume we're used to the heat

   2)  don't want to stop having fun

   3)  get impatient and say things like, "We're almost there. Let's just keep going," or "We just

        took a break."

   4)  et cetera


Symptoms of heat exhaustion are similar to but more intense than the symptoms of heat cramps. The line between heat cramps and exhaustion is blurry, but progression from one to the next means you are dehydrated or have lost too much salt from sweating.

   1)  headache  (an early sign of dehydration)

   2)  dizziness, lightheadedness

   3)  nausea, vomiting

   4)  cool, damp skin

   5)  muscle cramps

   6)  rapid heart rate

   7)  bright spots in your vision, followed by fainting


We have fainted while playing football and vomited while mountain biking. It happens to the best of us, and when it does, you can treat it the same way you would treat heat cramps: stop what you are doing, get out of the sun, sit down and rest, and drink lots of water or Gatorade (but never beer). If possible, jump in a pool or lake, lay in a creek, take a shower, or get inside where it is air conditioned.


3) Heat Stroke

No one is too tough to get heat stroke. No one can be "used to the heat." So once you have heat exhaustion, drinking water and Gatorade is not enough. If you drink up but do not stop what you are doing and get out of the sun and heat, your core body temperature will continue to rise and you will get heat stroke, which will wreck your internal organs and possibly kill you. 


If someone faints and does not wake up moments later, they have heat stroke. Other symptoms include:

   1)  absence of sweating

   2)  hot red or flushed dry skin

   3)  tiny pupils

   4)  rapid pulse

   5)  difficulty breathing

   6)  strange behavior

   7)  hallucinations / bright lights in vision

   8)  confusion

   9)  disorientation

   10)  seizure

   11)  coma


Heat stroke happens when your core body temperature reaches 104 or 105 degrees (depending on who you talk to). It is a medical emergency. and you must go to the hospital immediately. When someone's body temperature remains at 104 or above for more than a few minutes, they enter a death zone. Their organs shut down, the brain is damaged, and they never regain consciousness.


This is why heat stroke on the PCT will almost certainly be fatal. The trail is remote, and even if you get a cell signal, an EMS team will not be able to reach your location and get the person to a hospital in time. Also, while waiting for the EMTs, you will not be able to get the person indoors, into a shower, and dump ice on them, which will save their life. The best you could hope for is dragging the person into a creek or spring.


Fortunately, heat stroke is entirely preventable.


As PCT hikers traverse the desert in early spring and then enter the Sierras they experience a paradox: midday temperatures may hit 90+ degrees one day, only for a snow storm to hit the following day. Heat exhaustion and hypothermia are possible within the same 24 hours. 


The key to avoiding hypothermia on the PCT is to recognize and accept that it is a real possibility in the desert, no matter how hot it may get during the day. This is especially true in the early spring months of April and May. That means carrying rain gear and cold-weather clothes. Saving weight by bouncing them ahead to Kennedy Meadows (the start of the Sierras) is not worth the risk. 

For an in-depth review of hypothermia's symptoms, effects, treatments, et cetera, visit this page from Princeton University. We think it is important for hikers to know the symptoms for each stage of hypothermia. Page 167 of Cold: Adventures in the World's Frozen Places by Bill Streever has a incredible mnemonic device for remembering the signs of each stage,

The Umbles:

   First you mumble,

   then fumble,

   then grumble,

   then stumble,

   and finally tumble.

Does Cotton Kill in the Desert?

The expression "cotton kills" has been around for decades. While cotton is cool and comfortable against the skin, it can also hold a lot of water and dry very slowly. Since a cotton shirt soaks up sweat and then dries very slowly, it steals your body heat and makes you susceptible to hypothermia. But is this relevant in a desert with no humidity and temperatures between 90-100 degrees. Wouldn't absorbent, slow-drying clothes keep you cool? After all, that is why we sweat in the first place. 


This may come as a surprise, but cotton still kills in the desert. The primary reason: the first 700 miles of the PCT is a very windy place — the PCT even crosses two commercial wind farms. As the sun heats up the deserts in eastern California, hot air rises. Comparatively cooler air over the Pacific rushes in to fill the space left by the rising air. As a result there is almost always powerful wind coming from the west. Mountains then funnel that wind and intensify it. Despite a hot sun overhead, these winds can be quite cold, made colder still by wet clothes, and quickly rob you of body heat. This is one reason we recommend wearing wind-blocking nylon shirts and pants


Additionally, when you exert yourself (like while backpacking) and then stop, your body temperature can drop rapidly. Marathon runners know this, and after crossing the finish line runners are wrapped in thermal blankets to prevent hypothermia, even in summer. Wet cotton clothes exacerbate this problem and combined with the wind described above, are a recipe for hypothermia, even in the desert.


Dead Air

The key to warmth is to make sure air does not flow across your body. You do this by trapping air in small places close to your body to create "dead air." Your body warms this unmoving dead air and it keeps you warm. So in effect, it is not the clothing that keeps you warm but the air trapped by the clothing. Unlike cotton, synthetic fibers such as fleece (polyester) and nylon create dead air, even when wet, and they dry very quickly.

Knee Pain & Swelling

With every step hikers take, the weight of their backpacks comes crashing down onto their knees. Regardless of pre-hike training, nothing can prepare the knees for 6-8 hours of pounding every day for months on end. In the first month of a thru-hike, especially the first two weeks, knees swell and can become so painful and stiff you can hardly walk around.


The exact, medical prognosis of knee pain and swelling could be many things: a sprain or strain (tears of a tendon), tendinitis (inflammation triggered by overuse), Ilio-tibial band syndrome, or patellar compression syndrome (a dull, constant ache behind the kneecap).



Tendinitis, strains, and sprains are the most common problems during a hike and treatment in the field is pretty basic: stay off the leg for a few days, take it easy, eat lots of anti-inflammatory meds like ibuprofen. However, these problems can end your hike and send you home. Because of this, we prefer to focus on prevention, which is easy and requires only four things:

   1)  use trekking poles 

   2)  stretch your legs in the morning after warming up

   3)  go slow and do as low-mileage a day possible during the first two weeks 

        — long distances between water sources will make it impossible to do truly short days (6 miles, etc) 

   4)  eat ibuprofen in the evening during the first two weeks to prevent swelling overnight



Stretch every morning before leaving camp, or soon after leaving and briefly warming up. Your middle school PE coach might have taught you stretches that involve laying on the ground and bending the lower back, but don't do these. They are bad for your lower back, which will have a backpack filled with gear strapped to it all day. Instead, do these three standing stretches:


Bubonic Plague. Seriously, The Plague

The cause of the 14th century Europe's notorious Black Death is the bacterium Yersinia pestis, which lives in rodents, including ground squirrels and chipmunks, and is transmitted to people via fleas. In 2015, the bacterium was discovered in Yosemite National Park, including the Tuolumne Meadows Campground where many thru-hikers stay. Two people were infected, neither of whom were thru-hikers. That August the Park Service closed the Crane Flat and Tuolumne Meadows campgrounds in order to treat rodent burrows with an insecticide that kills fleas. No infections have been reported since.



The symptoms of plague are unambiguous. After the onset of fever, headache, chills, and weakness an infected person develops at least one very swollen and painful lymph node. Infection must be treated with antibiotics.


hantavirus cases by state / image via the CDC
hantavirus cases by state / image via the CDC

Yes, hantavirus.

The presence of hantavirus on the PCT and the AT seems to be a discussion many hikers don't want to have. During in-person conversations and on online forums we have experienced hikers dismissing hantavirus off-hand and refusing to admit it's present on either trail.

While the risk of infection is small, unfortunately, the virus is present. Here are the facts: 


What is Hantavirus?

Hantavirus is a family of viruses found in the Americas and Asia. While the virus usually infects rats and mice it does not lead to disease in rodents. Not every variation of the virus causes disease in humans, but a few North American strains can cause a respiratory condition called Hantavirus Pulmonary Syndrome (HPS), which is fatal 38% of the time. 


Signs & Symptoms

According to the CDC, the virus's incubation time is not positively known but it appears that symptoms develop 1 to 5 weeks after exposure to fresh urine, droppings, or saliva of infected rodents. Universal early symptoms include fever and muscle aches in the thighs, hips, back, and shoulders. Half of infected people experience headaches, dizziness, chills, nausea, vomiting, diarrhea, and abdominal pain.  As the disease progresses the lungs fill with fluid. 



In the American West, the virus lives within deer mice and appears in their urine, droppings, and saliva. However, the exact details of transmission to humans have not been discovered. Some researchers suspect you can get the virus by eating food contaminated with urine, droppings, or saliva or by touching a contaminated surface and then touching your nose or mouth.

What is certain is that HPS is a respiratory disease, and infection will take place if the virus is inhaled, which can happen when fresh rodent urine, droppings, or nesting materials become airborne, say by someone sweeping out a shelter. Fortunately, hantavirus is not  transmitted between people, like when touching or kissing. 

Likelihood of Infection on the PCT

It's slim. The desert is filled with rodents, as everyone who night-hikes discovers. However, the absence of AT-like shelters on the PCT is a blessing. Without shelters, hikers do not congregate in large groups at single locations where their crumbs and trash feed populations of mice and rats. Additionally, without shelters hikers do not sleep in structures where rodents feed and nest.


Instead, campsites are spread out along the Trail, and often there is room for just a few tents. Rodents populations are not as concentrated, and so the threat of hantavirus is pretty small.


The greatest risk of infection is in Yosemite National Park at one of the High Sierra Camps. In August of 2012 the National Park Service announced that there were three confirmed cases of hantavirus in Yosemite. By November there were ten cases and three people had died. Nine of the ten people were exposed to the virus while staying at the Signature Tent Cabins in Curry Village (15 miles from the PCT) and the tenth person was infected while hiking or staying at the High Sierra Camps, which are just off the PCT.


There has not been a reported outbreak since 2012 but if you are concerned about the virus, it's best not to stay at one of the High Sierra Camps. Most thru-hikers avoid the camps anyways because they are booked up long in advance and expensive to boot. 

Ass-to-Mouth Disease

You are your own biggest health-hazard in the backcountry. Outdoor novices worry about poison ivy, snakes et cetera, but if you get sick in the backcountry, you probably did it to yourself through poor hygiene. Tips for keeping clean are discussed on the sanitation page.

Water-Born Illnesses

Water sources on the PCT may contain bacteria, cysts, and parasites like fecal coliform bacteria, giardia, and even a brain-eating amoeba. These illnesses are discussed on the water treatment page. 

Insect-Born Disease

Mosquitoes and ticks are vectors for diseases that are discussed on the insects page.