What illness starts with aching legs? Identifying Potential Health Conditions

September 30, 2025 •

4 min read

Approximately one-third of people with fibromyalgia also experience restless legs syndrome, a neurological condition that can cause an irresistible urge to move the legs. However, this is just one of many potential health issues where aching legs can be an early symptom. Understanding the full context of your symptoms is crucial for identifying what illness starts with aching legs.

Quick Summary

This article explores common illnesses and conditions that can cause aching legs, such as viral infections, vascular issues, autoimmune diseases, and nerve problems. It outlines key differentiating symptoms and provides a guide on when leg pain may signal a more serious underlying health issue that requires medical attention.

Key Points

Identify the Cause: The illness starts with aching legs can range from common viral infections like the flu to serious conditions like Deep Vein Thrombosis (DVT).
Check for Other Symptoms: Leg aches from a viral illness are often accompanied by fever, fatigue, and other flu-like symptoms. In contrast, DVT often presents with unilateral leg swelling, warmth, and redness.
Consider Vascular Issues: Peripheral Artery Disease (PAD) causes leg cramps during activity (claudication) that resolve with rest, while venous insufficiency leads to aching, heavy legs.
Evaluate for Chronic Conditions: Conditions like fibromyalgia, lupus, and rheumatoid arthritis can cause chronic, widespread muscle or joint pain, including in the legs.
Watch for Nerve Pain: Sharp, radiating leg pain, numbness, or tingling can be signs of a nerve issue like sciatica or peripheral neuropathy.
Know When to Seek Emergency Care: Sudden, severe leg pain with swelling, warmth, or breathing difficulty requires immediate medical attention to rule out DVT or other urgent issues.

Common Causes of Aching Legs

Aching legs are a common complaint and can be a sign of many different underlying conditions, ranging from minor and temporary to chronic and severe. Pinpointing the cause requires a careful look at all accompanying symptoms.

Viral and Infectious Causes

Many viral and bacterial infections can trigger body aches, including in the legs, as a result of the immune system's response.

Influenza (Flu): One of the most common causes of illness-related leg pain. The flu often begins with a sudden onset of muscle or body aches, alongside fever, fatigue, headaches, and a cough. The aches are typically more severe than those with a common cold.
Viral Myositis: Caused by certain viruses like coxsackievirus, this is an inflammation of the muscles that can lead to significant leg pain.
Other Infections: Cellulitis (a skin infection) or Osteomyelitis (a bone infection) can also cause localized leg pain, often accompanied by redness, warmth, and swelling.

Vascular Problems

Blood flow issues are a significant source of leg pain, particularly for aching, heavy legs experienced at the end of the day or during rest.

Deep Vein Thrombosis (DVT): A serious condition involving a blood clot in a deep vein, most often in the leg. The pain from a DVT is typically in one leg and may feel like a cramp, but it gets progressively worse. Other symptoms include swelling, redness, and warmth in the affected leg.
Peripheral Artery Disease (PAD): This condition occurs when narrowed arteries reduce blood flow to the limbs. It causes muscle pain or cramping, known as claudication, during physical activity like walking. This pain typically subsides after a few minutes of rest.
Venous Insufficiency: Weakened valves in the leg veins cause blood to pool, leading to heavy, aching legs and potentially varicose veins.

Neurological Conditions

When nerves are compressed or damaged, they can produce pain, tingling, and weakness in the legs.

Sciatica: This occurs when the sciatic nerve is compressed or irritated, causing pain that radiates from the lower back down the back of one leg. The pain is often described as burning, sharp, or tingling.
Peripheral Neuropathy: Nerve damage from conditions like diabetes or alcoholism can lead to leg pain, numbness, and tingling.

Autoimmune and Inflammatory Diseases

Chronic inflammatory conditions can affect muscles, joints, and soft tissues throughout the body, including the legs.

Fibromyalgia: This chronic disorder causes widespread musculoskeletal pain, including deep, burning, or throbbing leg pain, along with fatigue, sleep problems, and cognitive issues.
Rheumatoid Arthritis (RA): While primarily affecting the joints, the systemic inflammation of RA can cause widespread pain and fatigue that may manifest in the legs.
Lupus: As a systemic autoimmune disease, lupus can cause inflammation in the muscles (myositis) and joints, leading to leg cramps and pain.

Comparison Table: Differentiating Common Causes


Feature	Viral Infection (Flu)	Deep Vein Thrombosis (DVT)	Peripheral Artery Disease (PAD)	Fibromyalgia	Sciatica
Onset	Sudden, with fever and other symptoms	Acute, persistent, worsening over time	Gradual, with exercise (claudication)	Gradual or triggered, chronic	Sudden, often after a specific movement
Location	Both legs, widespread muscle aches	Typically one leg (calf or thigh)	Calves, hips, or thighs, location-dependent	Widespread, often in thighs and upper arms	Radiates down one leg from the lower back
Sensation	Dull, achy, sore	Heavy, aching, cramping	Cramping, burning, aching	Deep, burning, throbbing	Sharp, burning, tingling
Relief	Rest, fluids, OTC meds	Elevation, but pain persists	Rest resolves pain (claudication)	Varies, complex management	Rest, but specific positions can worsen
Key Other Symptoms	Fever, cough, fatigue	Swelling, warmth, redness in one leg	Shiny skin, hair loss on legs, weak pulse	Fatigue, sleep issues, brain fog	Lower back pain, numbness, weakness

When Aching Legs Signal a Medical Emergency

While many causes are benign, certain symptoms require immediate medical attention. Seek emergency care if you experience any of the following:

Sudden, severe leg pain, swelling, warmth, or redness in one leg: These are hallmark signs of a Deep Vein Thrombosis (DVT), which can lead to a life-threatening pulmonary embolism if a blood clot travels to the lungs.
Leg swelling in both legs accompanied by breathing problems: This could signal a heart condition.
A leg that is pale or cooler than usual: This may indicate a problem with circulation.
Aching legs with fever and signs of infection, such as red streaks or tenderness: A severe infection like cellulitis or osteomyelitis needs prompt treatment.
Loss of bowel or bladder control alongside sciatica symptoms: This could indicate a rare but serious condition called cauda equina syndrome.

Understanding the Difference Between Soreness and Illness-Related Aches

It's important to distinguish between normal muscle soreness from exercise and aches caused by an underlying illness. Normal soreness, known as Delayed Onset Muscle Soreness (DOMS), typically occurs one to two days after physical activity and gradually improves. In contrast, illness-related aches may not be tied to exercise and are often accompanied by other systemic symptoms like fever or fatigue. Persistent or unexplained pain that does not improve with rest warrants a medical evaluation.

Conclusion

Aching legs are a symptom, not a diagnosis, and can signal a wide spectrum of health issues. From common viruses like the flu to more serious vascular and autoimmune conditions, the cause is dependent on the full clinical picture. While self-care can be effective for minor causes, recognizing when to seek professional medical advice is crucial for preventing complications from more serious illnesses like DVT. Always consider accompanying symptoms and the persistence of the pain when evaluating its potential cause.

For more information on when leg pain warrants a doctor's visit, consult the comprehensive guide from the Mayo Clinic.

Frequently Asked Questions

Aching legs can be a serious symptom if accompanied by sudden, severe pain, swelling, warmth, or redness in one leg. These can be signs of Deep Vein Thrombosis (DVT), a medical emergency. Other warning signs include a pale or cool leg, fever, or swelling in both legs with breathing problems.

Yes, viral infections like the flu commonly cause body and muscle aches, including in the legs, as a result of the immune system's inflammatory response. Flu-related aches tend to be more severe than those from a common cold.

Normal muscle soreness, or DOMS, appears after physical activity and usually resolves within a couple of days. Illness-related aches often have a more systemic feel, are not tied to exertion, and are accompanied by other symptoms like fever or fatigue.

Yes, nerve issues like sciatica, where the sciatic nerve is irritated, can cause radiating pain, burning, or tingling down one leg. Peripheral neuropathy, caused by nerve damage, can also lead to leg pain and numbness.

Yes, fibromyalgia is a chronic condition characterized by widespread pain, which can include deep, burning, or throbbing leg aches. This is often paired with fatigue and sleep difficulties.

With PAD, you may experience claudication, which is muscle pain or cramping in the legs (often the calves) during physical activity. The pain typically goes away after a few minutes of rest.

You should see a doctor if your leg pain is persistent, getting worse, occurs alongside swelling, redness, fever, or breathing issues. If pain comes on for no clear reason or home remedies don't help, a professional evaluation is recommended.