Raynaud's disease occurs when the small arteries (arterioles) that serve the fingers, toes, ears, or nose go into spasm. When arterioles go into spasm, they cut off blood supply and cause digits (fingers and toes) or the tips of the ears or nose to turn white or blue and lose feeling.

Sometimes this can happen as part of a pattern seen with other diseases, in which case it is called Raynaud's phenomenon or secondary Raynaud's. When this happens alone, without signs of any other underlying disease, it is called Raynaud's disease or primary Raynaud's.

People with Raynaud's phenomenon tend to get it either in both hands or in both feet. Raynaud's disease tends to appear in all of the hands and feet. About 3 out of 4 sufferers of primary Raynaud's disease are women aged between 15 and 40.

Everyone has two parallel nervous systems that do different jobs. The sympathetic nervous system speeds us up and prepares us for action. The parasympathetic nervous system calms us down and saves our energy. Raynaud's phenomenon and Raynaud's disease involve an overreaction by the sympathetic nervous system.

The effects of the sympathetic nervous system are felt most strongly when a sudden fright causes a rush of adrenaline. People who've been frightened feel their heart pounding and take deeper breaths. Others remark that they look as white as a sheet. This is because the body is preparing for "fight or flight" by constricting the outer blood vessels, reserving blood for the muscles and brain where it's most needed in an emergency. As the blood is pushed inwards, the skin turns white.

The sympathetic system reacts similarly when faced with cold temperature. Too much blood flowing through the blood vessels under the skin would radiate away vital body heat, so these outer vessels constrict and the blood is drawn inwards. Redness is seen as blood flows back out after coming in from the cold.

This is exactly what happens in Raynaud's, but the blood vessels of the fingers and toes constrict too tightly. Cold is the main trigger of Raynaud's attacks. Many people find attacks come on after reaching into the fridge, but cold touching another part of the body, like the back of the neck, can do it too. Strong emotion or shock causes attacks in a minority of sufferers.

In primary Raynaud's disease, we don't know why any of this happens. In secondary Raynaud's phenomenon, we can see it's linked to certain diseases but we still don't understand the exact mechanism.

Scleroderma is the disease most closely associated with Raynaud's phenomenon. The majority of people with scleroderma also have severe Raynaud's. Scleroderma is a chronic autoimmune disease that causes thickening and toughening of the skin and internal organ tissue.

A wide range of other diseases carry an elevated risk of Raynaud's:

• rheumatoid arthritis is a chronic autoimmune disease that causes debilitating pain and damage to the joints
• systemic lupus erythematosus (lupus) is a chronic autoimmune inflammatory disease of the skin and internal organs; like rheumatoid arthritis, scleroderma, and Raynaud's disease itself, lupus is much more common in women than in men
• atherosclerosis is a cardiovascular disease, also known as "hardening of the arteries"
• pulmonary hypertension is high blood pressure in the lungs, another cardiovascular disease
• hypothyroidism is decreased thyroid gland activity

You also have an increased risk of Raynaud's if you:

• smoke, because smoking makes attacks worse and may increase chances of getting Raynaud's in the first place (see our article on smoking cessation)
• suffer from migraines
• have nerve disorders
• have had an injury
• are exposed to vibrations, such as those caused by using heavy power tools
• have had frostbite
• type on a keyboard or play piano for many hours a day

Whatever the cause of Raynaud's, the symptoms are fairly common. The fingers or toes turn white, then blue, and start to lose feeling or the ability to move. It's rarely painful. The hand itself isn't normally affected, nor the thumb. Sometimes only parts of one or two fingers or toes are involved, and the skin turns a mottled red and white.

An attack brought on by cold usually ends when the hand or foot is warmed, but some attacks last hours. When an attack ends, the digits turn red for a while before resuming their normal appearance. There may be a "pins-and-needles" sensation.

That blue colour means the cells are being starved of oxygen. There's a tiny chance that a severe attack will lead to tissue death (necrosis). This is most likely, though still rare, in people with scleroderma.

If someone has fingers or toes that turn white, blue, and red at the slightest provocation, they may have Raynaud's. Further investigation is needed to determine whether it's primary Raynaud's or secondary to some other condition.

People may be tested for other diseases that are sometimes linked to Raynaud's phenomenon. If there's no evidence of other disease, injury, or drug reaction, and especially if the person is a woman under 40 years of age, they'll probably be diagnosed with primary Raynaud's disease.