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Vaso-occlusive crisis (VOC)is the most common reason people living with sickle cell disease (SCD) require emergency medical care. These episodes occur when sickled red blood cells obstruct small blood vessels, reducing oxygen delivery to tissues and triggering severe pain, inflammation, and, in some cases, organ damage.
While certain situations increase the likelihood of a crisis, it is important to understand one reassuring fact: not every pain crisis has an identifiable trigger. Even individuals who carefully follow medical advice may still experience episodes. Knowing the common risk factors, however, can help reduce the frequency and severity of crises.
Why does a sickle cell crisis happen?
Why does a sickle cell crisis happen?
Unlike healthy red blood cells, sickled cells are rigid, sticky, and less flexible. Under certain conditions, haemoglobin S (HbS) molecules lose oxygen and stick together (polymerize), causing red blood cells to adopt their characteristic sickle shape.
These abnormal cells interact with white blood cells, platelets, and the lining of blood vessels, creating inflammation and blockages that interrupt normal blood flow. The result is tissue ischemia (reduced oxygen supply), which causes the severe pain associated with a vaso-occlusive crisis.
Common triggers and why they matter
Common triggers and why they matter
Although triggers vary between individuals, several factors are consistently associated with an increased risk of crisis.
Although triggers vary between individuals, several factors are consistently associated with an increased risk of crisis.
Dehydration
Dehydration
When the body becomes dehydrated, blood becomes more concentrated and viscous. This increases the likelihood that sickled red blood cells will clump together and obstruct blood vessels.
Reduce your risk by: drinking adequate fluids throughout the day, particularly during hot weather, illness, or physical activity.
Infection
Infection
Infections are among the most important triggers of vaso-occlusive crises. Fever and infection increase inflammation, metabolic demand, and dehydration, all of which can promote sickling.
Reduce your risk by: staying up to date with recommended vaccinations, practising good hand hygiene, seeking prompt medical attention for fever, and taking prescribed preventive medications where appropriate.
Extreme temperatures
Extreme temperatures
Both very cold and very hot environments can contribute to a crisis.
Cold temperatures may cause blood vessels to constrict, reducing blood flow, while excessive heat increases fluid loss through sweating, leading to dehydration.
Reduce your risk by: dressing appropriately for the weather, avoiding prolonged exposure to extreme temperatures, and maintaining good hydration.
Low oxygen levels (Hypoxia)
Low oxygen levels (Hypoxia)
Anything that lowers oxygen levels, including severe asthma attacks, pneumonia, high-altitude travel, or untreated sleep-disordered breathing can increase red blood cell sickling.
Reduce your risk by: managing underlying respiratory conditions, seeking prompt treatment for breathing difficulties, and discussing travel to high-altitude locations with your healthcare provider.
Physical overexertion
Physical overexertion
Regular exercise is beneficial for overall health, but sudden, intense physical activity without adequate hydration or rest may increase the risk of a crisis in some individuals.
Reduce your risk by: exercising at a comfortable pace, staying hydrated, resting when needed, and avoiding strenuous activity when unwell.
Emotional and psychological stress
Emotional and psychological stress
Stress does not directly cause sickled cells to form. However, chronic psychological stress may contribute to inflammatory and hormonal changes that can increase vulnerability in some individuals.
Reduce your risk by: prioritising sleep, seeking emotional support, practising healthy stress-management techniques, and maintaining regular follow-up with your healthcare team.
Can every crisis be prevented?
Can every crisis be prevented?
Unfortunately, no.
Some vaso-occlusive crises occur without any obvious trigger. Sickle cell disease is a complex condition influenced by genetics, inflammation, blood vessel function, and individual biological differences. Experiencing a crisis does not necessarily mean that someone has done something wrong.
The goal of prevention is therefore risk reduction, not risk elimination.
Everyday habits that help reduce the risk of crisis
Everyday habits that help reduce the risk of crisis
Although there is no guaranteed way to prevent every episode, several evidence-based measures can significantly reduce complications:
Stay well hydrated.
Take prescribed medications consistently, including hydroxyurea if recommended.
Attend regular clinic appointments.
Keep vaccinations up to date.
Seek prompt treatment for fever or signs of infection.
Eat a balanced diet and get adequate sleep.
Exercise regularly but avoid overexertion.
Avoid smoking and exposure to tobacco smoke.
Learn your personal triggers and discuss them with your healthcare provider.
For many individuals, disease-modifying treatments such as hydroxyurea substantially reduce the frequency of vaso-occlusive crises and improve long-term health outcomes.
When should you seek urgent medical care?
When should you seek urgent medical care?
Pain should never be ignored simply because you have sickle cell disease.
Seek immediate medical attention if you experience:
Fever (38°C or higher)
Chest pain or difficulty breathing
Sudden weakness, confusion, or difficulty speaking
Severe pain that does not improve with your prescribed home treatment
Persistent vomiting or inability to drink fluids
A painful erection lasting more than four hours (priapism)
Early treatment can prevent serious complications and improve recovery.
Key Takeaway & Conclusion
Key Takeaway & Conclusion
Living with sickle cell disease means understanding your body, not fearing it. While not every pain crisis can be prevented, recognising common triggers, maintaining healthy daily habits, and receiving regular specialist care can significantly reduce the risk of complications and improve quality of life.
The goal is not perfection, it is preparation.
References
References
World Health Organization. (2025). Sickle Cell Disease https://www.who.int/news-room/fact-sheets/detail/sickle-cell-disease
Darbari, D. S., Sheehan, V. A., & Ballas, S. K. (2020). The vaso-occlusive pain crisis in sickle cell disease: Definition, pathophysiology, and management. European Journal of Haematology, 105(3), 237–246. https://doi.org/10.1111/ejh.13430 https://pubmed.ncbi.nlm.nih.gov/32301178/
Yawn, B. P., Buchanan, G. R., Afenyi-Annan, A. N., et al. (2014). Management of sickle cell disease: Summary of the 2014 evidence-based report by expert panel members. JAMA, 312(10), 1033–1048. https://doi.org/10.1001/jama.2014.10517 https://pubmed.ncbi.nlm.nih.gov/25203083/
Osunkwo, I., Andemariam, B., Minniti, C. P., et al. (2021). Contemporary management and prevention of vaso-occlusive crises (VOCs) in adults with sickle cell disease. Journal of Pharmacy Practice, 35(5), 808–820. https://doi.org/10.1177/08971900211026644 https://pubmed.ncbi.nlm.nih.gov/34151636/
Solomon, L. R. (2008). Treatment and prevention of pain due to vaso-occlusive crises in adults with sickle cell disease: An educational void. Blood, 111(3), 997–1003. https://doi.org/10.1182/blood-2007-07-089144 https://pubmed.ncbi.nlm.nih.gov/17940207/
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