The sensation of cold knees is often temporary but can signal changes in the body’s internal function. This localized coldness relates directly to the body’s mechanism for maintaining core temperature. When the body detects a drop in temperature, it initiates peripheral vasoconstriction, narrowing small blood vessels near the skin surface. This redirects warm blood away from the limbs and toward the core organs. The resulting reduced blood flow to the knee area makes the skin feel cool to the touch.
Local and Environmental Factors
The most common reasons for cold knees are linked to the surrounding environment and daily habits. Exposure to cold air, such as from an air conditioner or winter weather, triggers a normal vasoconstriction response. Since the knee joint has less insulating fat and muscle compared to the thigh, it is more susceptible to rapid temperature loss, making the area feel notably colder.
Simple behaviors can also temporarily impede local circulation around the knee. Sitting with legs crossed tightly or wearing restrictive clothing, like very tight jeans, places pressure on blood vessels. This temporary compression slows the delivery of warm blood, leading to a transient cold feeling that resolves quickly upon changing position.
Issues Affecting Blood Flow
When cold knees are chronic and persist regardless of a warm environment, the cause may relate to conditions that physically reduce blood flow. Peripheral Artery Disease (PAD) is a significant example, characterized by the buildup of fatty plaque within the arteries of the legs. This atherosclerosis narrows the arteries, restricting the volume of oxygenated, warm blood that can reach the knee and lower leg. The resulting coldness is a genuine drop in physical temperature due to poor circulation.
The coldness from PAD is often accompanied by other symptoms, such as leg pain or cramping during exercise, known as claudication. Systemic conditions affecting overall circulation can also contribute to the cold sensation. For instance, severe hypothyroidism, an underactive thyroid, slows the body’s metabolism and heart rate, which can lead to a less efficient distribution of blood and a generalized intolerance to cold.
Another circulatory issue is Raynaud’s phenomenon, which causes episodes of extreme vasoconstriction, typically in the fingers and toes, but occasionally affecting the legs. This condition involves small arteries going into spasm, severely limiting blood flow in response to cold or stress. Additionally, anemia reduces the body’s ability to carry oxygen due to a lack of healthy red blood cells, contributing to poor thermal regulation.
Neural Causes of Cold Sensation
Sometimes, the feeling of coldness is not due to the knee’s actual temperature but rather a miscommunication within the nervous system. This is often the result of peripheral neuropathy, which is damage to the sensory nerves that transmit information to the brain. Damaged nerves send abnormal signals, such as tingling, numbness, or a sensation of extreme cold, even if the knee is warm to the touch.
Diabetes is a leading cause of peripheral neuropathy, where high blood sugar levels damage nerve fibers over time. This damage can begin in the longest nerves, affecting the feet and legs first, including the area around the knee. Similarly, a severe deficiency in Vitamin B12 can also lead to peripheral neuropathy, as the vitamin is vital for nerve health and the protective myelin sheath surrounding nerve fibers.
Nerve compression or entrapment near the knee joint or in the lower spine can also irritate a nerve and cause localized cold sensations. A pinched nerve, such as from a herniated disc in the lower back, may cause referred sensations of coldness or pain that travel down the leg to the knee area.
When to Seek Medical Advice
If the coldness in your knees is persistent, occurs in only one leg, or is accompanied by other troubling symptoms, medical evaluation is warranted. Red flags indicating a potential circulatory problem include skin color changes, such as paleness or a bluish tint, and the presence of non-healing sores or ulcers on the lower leg or foot. Significant pain, particularly cramping that occurs while walking and resolves with rest, is a classic sign of PAD that requires prompt attention.
To assess for PAD, a doctor may perform an Ankle-Brachial Index (ABI) test, which compares blood pressure in the ankle to the blood pressure in the arm. An ABI value below 0.9 suggests reduced blood flow and is diagnostic for PAD. For suspected neural causes, blood tests can check for underlying systemic issues, including uncontrolled diabetes, severe thyroid dysfunction, or Vitamin B12 deficiency.