What are the complications of dengue fever?

Dengue fever has a way of misleading people at the start. The first few days can feel like a brutal flu: high fever, pounding headache, deep muscle and joint aches, nausea, and an exhaustion that makes even basic tasks feel heavy. In places where dengue is common, many people ride it out at home, expecting the fever to break and recovery to begin. The complication is that dengue does not always follow a simple arc. In some cases, the illness becomes most dangerous right when the fever starts to settle. That timing is one reason dengue continues to strain hospitals across the region: it can look manageable until the body enters a short critical phase where complications escalate quickly.

The most serious complications of dengue revolve around how the virus and the immune response affect blood vessels, circulation, and organ function. Dengue can increase the permeability of small blood vessels for a limited period. When that happens, fluid that should remain in the bloodstream can leak into surrounding tissues and body cavities. This fluid shift matters more than it sounds. The bloodstream is not just a transport system for oxygen and nutrients. It is also the engine of blood pressure and organ perfusion. When the effective circulating volume drops, the heart and blood vessels try to compensate by increasing heart rate and tightening peripheral circulation. At first, a person may still appear relatively stable. But if leakage continues, the body can tip into shock.

Shock in dengue is not the dramatic movie version where someone collapses instantly. It can build in a deceptively quiet way. Someone might look pale and feel clammy. They may complain of dizziness, restlessness, or a sudden sense of weakness that feels different from ordinary fatigue. Their hands and feet may feel cold. Urine output can drop because the kidneys are not getting enough perfusion. Breathing may feel slightly more laboured if fluid begins collecting around the lungs, or if the body is struggling to compensate for poor circulation. Once shock progresses, it can become a medical emergency within hours. This complication is often described as dengue shock syndrome, and it is one of the clearest dividing lines between uncomplicated dengue and severe dengue.

Bleeding is another feared complication, and it also exists on a spectrum. Mild bleeding might show up as easy bruising, small pinpoint spots on the skin, or gum and nose bleeding. More severe bleeding can involve the gastrointestinal tract, where vomiting blood or passing black, tarry stools signals internal bleeding. In dengue, bleeding risk is influenced by multiple factors, including low platelet counts, disruption of clotting function, and fragile blood vessels affected by inflammation. Platelets often become a focal point in casual dengue conversations, but the reality is more nuanced. A low platelet count can raise concern, yet the overall risk of severe outcomes is tied to the broader clinical picture: warning signs, hydration status, signs of plasma leakage, changes in blood pressure, and evidence of organ stress.

What makes bleeding particularly dangerous in dengue is how it can interact with shock. If a person is already losing effective circulating volume due to plasma leakage, bleeding further reduces the oxygen-carrying capacity and destabilises circulation. The body’s compensatory mechanisms can fail quickly. This is why clinicians treat significant bleeding in dengue as urgent, especially if it comes with abdominal pain, persistent vomiting, or a sudden decline in alertness. It is not simply a matter of waiting for the fever to pass. It is a matter of preventing the body from sliding into a spiral that becomes harder to reverse.

Beyond circulation and bleeding, severe dengue can also involve organ impairment. The liver is commonly affected, sometimes showing elevated enzymes that signal inflammation or injury. In more severe cases, the liver can become significantly inflamed, and this can contribute to fatigue, nausea, abdominal discomfort, and metabolic instability. The kidneys can suffer when blood pressure and perfusion fall, or when dehydration and systemic inflammation strain their filtration function. Reduced urine output is not just an inconvenience. It can be a sign that the kidneys are struggling and the body is not maintaining stable circulation.

The brain and nervous system can also be affected, either directly through inflammatory processes or indirectly through shock, metabolic disturbances, or severe dehydration. This can present as confusion, unusual sleepiness, irritability, or difficulty staying alert. The heart, too, may become involved in rare cases, where inflammation affects heart muscle function and makes the body less able to compensate for fluid shifts. When multiple organs show signs of strain, the illness is no longer just a viral fever. It becomes a systemic crisis that requires close monitoring and supportive medical care.

One of the most important practical points about dengue complications is their timing. Many people assume danger is highest when the fever is at its peak. With dengue, the opposite can sometimes be true. The critical phase often begins around the time the fever comes down. That moment can feel like relief, but it is also when plasma leakage and the risk of shock can emerge. The body may look like it is improving, while the internal balance of fluids and circulation is becoming unstable. This is why clinicians pay close attention to warning signs that appear after the fever settles: severe abdominal pain, persistent vomiting, bleeding from the nose or gums, vomiting blood, blood in stool, sudden restlessness or extreme fatigue, faintness when standing, and reduced urine output. These signals are less about discomfort and more about physiology. They can indicate that circulation is slipping or that the body is entering a dangerous phase.

Dengue can also produce complications related to fluid accumulation. As plasma leaks, fluid can collect in the abdomen or around the lungs. A person might feel bloated, unusually full, or short of breath. Even mild breathlessness should not be brushed off in suspected dengue, especially if it appears alongside other warning signs. Fluid shifts are part of what makes dengue monitoring so meticulous in hospitals: care teams watch how much a patient drinks, how much urine they pass, changes in vital signs, and laboratory trends that suggest haemoconcentration or evolving instability. This is also why “aggressive hydration” is not a simple home remedy. Hydration matters, but in severe dengue the body’s handling of fluids becomes tricky. Too little fluid worsens dehydration and shock risk. Too much fluid at the wrong time can contribute to overload once the leaked fluid begins returning to circulation during recovery. Proper management is about balance, not just volume.

Certain groups may face higher stakes if complications occur. Young children can deteriorate faster because they have less physiological reserve and may not communicate symptoms clearly. Older adults may have underlying conditions that make them less tolerant of dehydration or blood pressure shifts. Pregnant women require careful monitoring because dengue complications can intersect with bleeding risk and the demands of pregnancy. These situations do not mean severe dengue is inevitable, but they do mean the threshold for assessment and observation is lower.

None of this is meant to turn every dengue scare into panic. Most people recover, and supportive care is often enough. But dengue’s complications deserve respect because they are predictable in pattern, concentrated in a short window, and potentially severe. The best protection is not fear. It is attentiveness to the timing of symptoms and the warning signs that suggest the illness is changing character. If dengue is suspected or confirmed, the days around the fever’s resolution should be treated as a period of careful observation. If warning signs appear, or if a person seems to worsen suddenly even as the fever drops, medical evaluation is essential.

In the end, dengue is a reminder that not all fevers behave the same way. Some illnesses peak and then fade. Dengue can pivot. Its complications arise from fluid leakage, bleeding risk, and organ stress, and they can unfold quickly during the critical phase. Knowing that pattern helps people act sooner, seek care when it matters, and avoid the false reassurance that comes with a falling temperature. In dengue, feeling better is welcome, but it is not always the finish line.