Having bloody or red eyes after exercise is not uncommon. In most cases, the problem isn't serious. But there is the possibility that an underlying medical disorder, such as high blood pressure, could be the cause. Other common, less-worrisome causes include straining during exercise and irritants such as dust or sweat. In some cases, a heavy pressure can cause the blood vessels of the eye to burst -- a condition known as subconjunctival hemorrhage. In most cases, the problem clears up in 10 to 14 days.
Exercise
Cardio exercise by itself should not cause either bloody eyes or red eyes. The cause is usually either an external irritant or an underlying systemic disorder made worse by the cardio. If, however, you are including weight training as part of your workout, that may be the cause. Weight training can put enormous pressure on your muscles and blood vessels, especially if you are holding your breath while lifting. The vessels in the eye are particularly small and susceptible to breaking.
Hypertension
Hypertension, or high blood pressure, usually has no identifiable cause -- although it can be secondary to another underlying condition. If you suffer from hypertension, you may not have any symptoms and it may only be detected when you have your blood pressure measured. Your high blood pressure may come to light during strenuous cardio exercise because of the increased blood flow caused by your heart pumping faster. If you have high blood pressure you may have weakened blood vessels, and the temporary increase in pressure can make the thin, weaker blood vessels in the eye break, leading to a subconjunctival hemorrhage. Consult your doctor to verify your blood pressure is within the proper range.
Irritants
Red or bloody eyes could be the result of something irritating your eyes, particularly if you perform your cardio outdoors. Pollen, dust and even your own sweat can irritate your eyes and cause inflammation. If you are wearing cologne or sunscreen, this could make it worse, possibly causing an allergic reaction. Contacts are another common cause of irritation in the eye, which is made worse by exercise and sweating. Try exercising without your contacts if this is the case. Consult a doctor to test for possible allergies.
Considerations
In most cases, bloody or red eyes will clear up on their own. Using over-the-counter eye drops may help relieve or reduce the problem. If you find that you consistently have bloody eyes after or during exercise, or if the problem doesn't clear up after 10 to 14 days, consult an ophthalmologist. You may have a problem with your eyes, such as a episcleritis -- a non-infectious irritation of the eye lining. Certain medications can also cause changes in your blood pressure, leading to bloody or red eyes. Discuss any medications you are taking with your doctor. In rare cases, your bloody eyes may be caused by an underlying systemic problem such as hyperthyroidism.
