Signs and Symptoms of Mountain Sickness

I. The Silent Challenge: What Happens to Your Body at Altitude

At sea level, the air you breathe is approximately 21% oxygen. As you ascend, the percentage remains the same, but the atmospheric pressure drops — meaning each breath contains fewer oxygen molecules. At the summit of Kilimanjaro (5,895 metres), the effective oxygen availability is only about 47–50% of what it is at sea level. Your body responds with a complex set of physiological adjustments: you breathe faster and deeper (the hypoxic ventilatory response), your heart rate increases, and over days, your kidneys excrete bicarbonate to make your blood slightly more acidic, which stimulates further breathing. Your body also produces more red blood cells — but this takes weeks, not days, and offers little benefit on a typical one‑week climb.

The problem on Kilimanjaro is speed. The mountain's routes ascend far faster than the body can naturally acclimatise. A typical 7‑day Machame climb ascends from 1,800 metres to 5,895 metres in less than a week — a rate that exceeds the ability of many climbers' bodies to adapt. This is why route length is the single most important factor in summit success and safety: an 8‑day or 9‑day route gives your body approximately 25–40% more acclimatisation time than a 6‑day route, and the difference in AMS incidence is dramatic. Mountain sickness is not a binary condition — it exists on a spectrum from mild discomfort to life‑threatening illness. Understanding that spectrum is the first step toward managing it.

II. Acute Mountain Sickness (AMS): The First Warning

Acute Mountain Sickness (AMS) is the most common form of altitude illness. It is not in itself life‑threatening, but it must be taken seriously — because untreated AMS can progress to the far more dangerous HAPE or HACE. The hallmark symptom is a headache — typically throbbing, often described as a band tightening across the forehead, and usually worse at night or on waking. The headache of AMS is not a dehydration headache; it is caused by the swelling of blood vessels in the brain as your body struggles to maintain oxygen delivery, and it is often resistant to simple painkillers alone.

Beyond headache, AMS is defined by at least one of the following symptoms, appearing within 6–12 hours of reaching a new altitude: loss of appetite, nausea, or vomiting (the gut is particularly sensitive to hypoxia), fatigue or weakness out of proportion to exertion, dizziness or light‑headedness, and difficulty sleeping — often characterised by frequent waking, a sensation of breathlessness at night (periodic breathing), and strange dreams. The Lake Louise AMS Score, used by guides worldwide, rates each of four symptoms — headache, gastrointestinal upset, fatigue, and dizziness — on a scale of 0 (none) to 3 (severe). A total score of 3 or more, in the presence of a headache and recent ascent, indicates AMS. Mild AMS (score 3–5) usually responds to rest, hydration, and simple analgesia. Moderate AMS (score 6–9) requires stopping ascent and considering descent. Severe AMS (score 10–12) mandates immediate descent.

III. High Altitude Pulmonary Edema (HAPE): When Your Lungs Fill with Fluid

High Altitude Pulmonary Edema (HAPE) is the most common fatal form of altitude illness. It occurs when the low oxygen environment causes the blood vessels in the lungs to constrict unevenly, forcing fluid from the capillaries into the air sacs of the lungs. The result is a climber literally drowning in their own body fluids — a process that can kill within hours if untreated. HAPE can develop on its own or as a progression from untreated AMS. It is more common in people who ascend rapidly, those with pre‑existing respiratory conditions, and — crucially — individuals who have had HAPE before, who have a roughly 60% chance of recurrence on re‑ascent.

The early signs of HAPE are deceptively subtle. The climber may simply feel more breathless than expected for the altitude and exertion level. This breathlessness — dyspnoea — progresses from occurring only with effort to occurring at rest, a sign known as dyspnoea at rest that is an absolute red flag. The climber develops a dry cough that may progress to a productive cough bringing up pink, frothy sputum — the classic and terrifying sign of fulminant HAPE. Listening to the chest with a stethoscope (or even an ear pressed against the back) may reveal crackles or gurgling sounds — the sound of fluid in the lungs. Other signs include cyanosis (a blue or grey tint to the lips and nail beds, indicating severe oxygen deprivation), chest tightness, a rapid heart rate (tachycardia), and a low‑grade fever. A pulse oximeter reading that drops below 70–75% at rest at high camp is cause for serious concern; below 60%, emergency descent is mandatory.

There is one critical fact about HAPE that every Kilimanjaro climber must know: descent is the only definitive treatment. A descent of just 500–1,000 metres can be life‑saving. Oxygen, nifedipine (a calcium channel blocker that reduces pulmonary artery pressure), and a portable hyperbaric chamber (Gamow bag) can buy time, but nothing replaces getting the patient to a lower altitude as rapidly as possible. A climber who cannot walk must be carried — by porters, by stretcher, by any means necessary.

IV. High Altitude Cerebral Edema (HACE): The Brain Under Siege

If HAPE is the most common fatal altitude illness, High Altitude Cerebral Edema (HACE) is the most terrifying. It occurs when the brain swells with fluid — a direct result of severe hypoxia — and it can progress from mild confusion to coma and death within 12–24 hours. HACE is often preceded by worsening AMS, but it can also strike with frightening speed in a climber who seemed well just hours earlier. The earliest and most important sign is ataxia — a loss of coordination, particularly a staggering walk. The classic field test is the heel‑to‑toe walking test: ask the person to walk a straight line, placing the heel of one foot directly against the toes of the other. A person with early HACE will be unable to do this — they will stumble, sway, or fall. This test is simple, requires no equipment, and is one of the most reliable early indicators of a life‑threatening neurological crisis.

As HACE progresses, the symptoms become unmistakable: severe headache unresponsive to painkillers, confusion and disorientation (the person may not know where they are or what day it is), hallucinations (visual or auditory), extreme lethargy or drowsiness, and ultimately loss of consciousness and coma. The person may become irritable, uncooperative, or irrational — behaviour that friends and fellow climbers may misinterpret as stress or exhaustion, with fatal consequences. Any alteration in mental status at altitude is HACE until proven otherwise. Treatment is immediate, maximum‑speed descent. Dexamethasone (a potent steroid that reduces brain swelling) can be administered as a temporary measure, and oxygen should be given if available. But like HAPE, the only definitive cure is to get the patient to a lower altitude. Without descent, HACE is uniformly fatal.

V. The Golden Rule: Descent Is the Only Cure

There is a single principle that underlies every piece of medical advice on altitude illness, and it is this: if symptoms are severe, worsening, or not responding to treatment, go down. No drug — not Diamox, not dexamethasone, not nifedipine — can substitute for the simple act of reducing altitude. A descent of just 300–500 metres can reverse the symptoms of AMS. A descent of 1,000 metres can save a life in HAPE or HACE. The decision to descend is difficult — it means abandoning a summit attempt, disappointing a group, confronting the reality that your body has said no. But it is never the wrong decision. The summit will still be there next year. You may not be, if you ignore the warning signs. The mantra on Kilimanjaro should be: "If in doubt, go down." A good guide will insist on it. A great climber will accept it without argument. Kilimanjaro does not punish those who turn back. It punishes those who do not.

VI. Prevention: How to Give Your Body the Best Chance

The best treatment for mountain sickness is never to develop it in the first place. While no strategy guarantees immunity — there is simply no way to predict how your body will respond to altitude — several proven measures dramatically reduce your risk. The single most effective strategy is slow ascent. Choose a route of at least 7 days, ideally 8–9 days. The Lemosho 8‑day and Northern Circuit 9‑day routes give your body time to acclimatise and have the highest summit success rates and lowest AMS incidence on the mountain. On any route, follow the "climb high, sleep low" principle: your daily trek may take you to a higher altitude, but you should sleep at the lowest practical point. This is why the Machame route's day from Shira Camp to Lava Tower (4,630m) and then down to Barranco Camp (3,976m) is so effective — it forces a powerful acclimatisation response without exposing you to a dangerous sleeping altitude.

Beyond route selection, pharmacological prophylaxis with acetazolamide (Diamox) is widely recommended. Diamox works by inhibiting the enzyme carbonic anhydrase, causing the kidneys to excrete bicarbonate and making the blood slightly more acidic. This stimulates increased ventilation — you breathe more, particularly at night, improving oxygenation. The standard prophylactic dose is 125 mg twice daily, starting the day before ascent and continuing until descent begins. Side effects include tingling in the fingers and toes, a metallic taste in the mouth, and increased urination — all normal and generally mild. Diamox is a sulfonamide; those with sulfa allergies should consult their doctor. It is available in Moshi pharmacies, but it is strongly recommended to obtain it before travelling and to trial it at home to ensure you tolerate it well.

Other essential prevention strategies: hydrate aggressively — aim for 3–4 litres of water per day, using the colour of your urine (pale straw is ideal) as a guide. Eat plenty of carbohydrates, which require less oxygen to metabolise than fats or proteins and help fuel the increased respiratory effort. Avoid alcohol, sedatives, and sleeping pills, which depress respiration and can dangerously exacerbate the hypoxia of sleep at altitude. Walk slowly — the Swahili mantra "pole pole" (slowly, slowly) is not merely cultural advice; it is a physiological necessity. And if you have the opportunity, pre‑acclimatise by climbing Mount Meru (4,566m) or spending several days at altitude before beginning your Kilimanjaro ascent.

VII. Treatment: What to Do When Symptoms Strike

When symptoms of mountain sickness appear, the response must be immediate and systematic. For mild AMS: Stop ascending. Rest at the current altitude. Hydrate. Take paracetamol (acetaminophen) or ibuprofen for headache. Anti‑emetics (such as ondansetron or promethazine) can help with nausea. Monitor the Lake Louise score. If symptoms resolve within 24 hours, ascent may continue cautiously. If symptoms persist or worsen, descent is mandatory. For moderate AMS: Descent of at least 300–500 metres. If descent is not immediately possible, supplemental oxygen (2–4 litres per minute) and acetazolamide (250 mg twice daily) can be administered while descent is arranged. Dexamethasone (4–8 mg every 6 hours) may be considered in severe cases. For HAPE: Immediate descent is the priority. Administer oxygen (4–6 litres per minute) if available. Nifedipine (30 mg extended‑release every 12 hours) can reduce pulmonary artery pressure and buy time. A portable hyperbaric chamber (Gamow bag) can simulate descent by increasing pressure around the patient. For HACE: Immediate, maximum‑speed descent. Dexamethasone (8 mg initially, then 4 mg every 6 hours) is the emergency drug. Oxygen if available. Do not wait until morning. Do not wait for the guide to agree. Descend now.

VIII. Kilimanjaro‑Specific Realities: What Every Climber Must Understand

Kilimanjaro presents a unique altitude challenge. Unlike most high mountains, where climbers spend weeks acclimatising through progressively higher camps, Kilimanjaro's routes ascend rapidly — far faster than the body's natural adaptation mechanisms. This is why the mountain has a higher incidence of AMS than many technically harder peaks. The guides of Kilimanjaro are among the most experienced altitude managers in the world, but they cannot control the weather, the route, or your individual physiology. They rely on you to report your symptoms honestly. The culture of summit‑at‑all‑costs can be dangerous; a climber who hides a headache out of embarrassment or competitive drive is a climber at risk. At African Majestic Adventure, our guides are Wilderness First Responder certified and carry pulse oximeters, oxygen, and comprehensive medical kits on every single trek. They conduct twice‑daily health checks using the Lake Louise AMS score. They have the training, the equipment, and the authority to make the decision to descend — and they will do so without hesitation if your safety demands it. Trust them. They have climbed this mountain more times than you have had birthdays, and their only priority is getting every member of the team down safely.

IX. Final Verdict: Knowledge Is Your Oxygen

Mountain sickness is not a mystery. It is a predictable, well‑studied physiological response to the thin air of high altitude — and with the right preparation, the right route, and the right mindset, it is a risk that can be managed. The climbers who get into trouble on Kilimanjaro are not the ones who are unfit or inexperienced. They are the ones who ignore the headache, who hide the nausea, who push through the dizziness because the summit beckons and the cost of the trip feels too high to waste. Do not be that climber. Learn the symptoms. Monitor yourself and your companions. Trust your guide. And if the mountain tells you to stop — stop. The summit of Kilimanjaro is one of the greatest experiences a human being can have. But it is not worth your life. Climb with knowledge, climb with humility, and climb with a company that puts your safety above its summit statistics.