All Diseases

Deep vein thrombosis (DVT) occurs when a blood clot (thrombus) forms in one or more of the deep veins in your body, usually in your legs. Deep vein thrombosis can cause leg pain or swelling, but may occur without any symptoms.

Deep vein thrombosis can develop if you have certain medical conditions that affect how your blood clots. Deep vein thrombosis can also happen if you don't move for a long time, such as after surgery, following an accident, or when you are confined to a hospital or nursing home bed.

Deep vein thrombosis is a serious condition because blood clots in your veins can break loose, travel through your bloodstream and lodge in your lungs, blocking blood flow (pulmonary embolism).

Dehydration occurs when you use or lose more fluid than you take in, and your body doesn't have enough water and other fluids to carry out its normal functions. If you don't replace lost fluids, you will get dehydrated.

Common causes of dehydration include vigorous exercise, especially in hot weather; intense diarrhea; vomiting; fever or excessive sweating. Not drinking enough water during exercise or in hot weather even if you're not exercising also may cause dehydration. Anyone may become dehydrated, but young children, older adults and people with chronic illnesses are most at risk.

You can usually reverse mild to moderate dehydration by drinking more fluids, but severe dehydration needs immediate medical treatment. The safest approach is preventing dehydration in the first place. Keep an eye on how much fluid you lose during hot weather, illness or exercise, and drink enough liquids to replace what you've lost.

Delayed ejaculation — sometimes called impaired ejaculation — is a condition in which it takes an extended period of sexual stimulation for a man to reach sexual climax and release semen from the penis (ejaculate). Some men with delayed ejaculation are unable to ejaculate at all.

Delayed ejaculation can be temporary or a lifelong problem. Possible causes of delayed ejaculation include certain chronic health conditions, surgeries and medications. Treatment for delayed ejaculation depends on the underlying cause.

It's normal for men to have delayed ejaculation from time to time. Delayed ejaculation is only a problem if it's ongoing or causes stress for you or your partner.

Delirium is a serious disturbance in a person's mental abilities that results in a decreased awareness of one's environment and confused thinking. The onset of delirium is usually sudden, often within hours or a few days.

Delirium can often be traced to one or more contributing factors, such as a severe or chronic medical illness, medication, infection, surgery, or drug or alcohol abuse.

The symptoms of delirium and dementia can be similar, and input from a family member or caregiver may be important for a doctor to make an accurate diagnosis.

Dementia isn't a specific disease. Instead, dementia describes a group of symptoms affecting memory, thinking and social abilities severely enough to interfere with daily functioning.

Dementia indicates problems with at least two brain functions, such as memory loss and impaired judgment or language, and the inability to perform some daily activities such as paying bills or becoming lost while driving.

Though memory loss generally occurs in dementia, memory loss alone doesn't mean you have dementia. There is a certain extent of memory loss that is a normal part of aging.

Many causes of dementia symptoms exist. Alzheimer's disease is the most common cause of a progressive dementia. Some causes of dementia may be reversible.

Dengue (DENG-gey) fever is a mosquito-borne disease that occurs in tropical and subtropical areas of the world. Mild dengue fever causes high fever, rash, and muscle and joint pain. A severe form of dengue fever, also called dengue hemorrhagic fever, can cause severe bleeding, a sudden drop in blood pressure (shock) and death.

Millions of cases of dengue infection occur worldwide each year. Dengue fever is most common in Southeast Asia and the western Pacific islands, but the disease has been increasing rapidly in Latin America and the Caribbean.

Researchers are working on dengue fever vaccines. For now the best prevention is to reduce mosquito habitat in areas where dengue fever is common.

Depersonalization-derealization disorder occurs when you persistently or repeatedly have the feeling that you're observing yourself from outside your body or you have a sense that things around you aren't real, or both. Feelings of depersonalization and derealization can be very disturbing and may feel like you're living in a dream.

Many people have a passing experience of depersonalization or derealization at some point. But when these feelings keep occurring or never completely go away, it's considered depersonalization-derealization disorder. This disorder is more common in people who've had traumatic experiences.

Depersonalization-derealization disorder can be severe and may interfere with relationships, work and other daily activities. The main treatment for depersonalization-derealization disorder is talk therapy (psychotherapy), although sometimes medications also are used.

Depression is a mood disorder that causes a persistent feeling of sadness and loss of interest. Also called major depression, major depressive disorder or clinical depression, it affects how you feel, think and behave and can lead to a variety of emotional and physical problems. You may have trouble doing normal day-to-day activities, and depression may make you feel as if life isn't worth living.

More than just a bout of the blues, depression isn't a weakness, nor is it something that you can simply "snap out" of. Depression may require long-term treatment. But don't get discouraged. Most people with depression feel better with medication, psychological counseling or both. Other treatments also may help.

Dermatitis is a general term that describes an inflammation of the skin. Dermatitis can have many causes and occurs in many forms. It usually involves an itchy rash on swollen, reddened skin.

Skin affected by dermatitis may blister, ooze, develop a crust or flake off. Examples of dermatitis include atopic dermatitis (eczema), dandruff, and rashes caused by contact with any of a number of substances, such as poison ivy, soaps and jewelry with nickel in it.

Dermatitis is a common condition that's not contagious and usually isn't life-threatening. Even so, it can make you feel uncomfortable and self-conscious. A combination of self-care steps and medications can help you treat dermatitis.

Dermatographia is a condition also known as skin writing. When people who have dermatographia lightly scratch their skin, the scratches redden into a raised wheal similar to hives. These marks usually disappear within 30 minutes.

The cause of dermatographia is unknown, but it can be triggered in some people by infections, emotional upset or medications such as penicillin.

Most people who have dermatographia don't seek treatment. If your signs and symptoms are especially bothersome, your doctor may recommend allergy medications such as diphenhydramine (Benadryl).