Oedema is swelling caused by too much fluid trapped in the body’s tissues. There are six factors that can contribute to the formation of oedema:
1. Increased hydrostatic pressure
2. Reduced colloidal or oncotic pressure within blood vessels
3. Increased tissue colloidal or oncotic pressure
4. Increased blood vessel wall permeability (such as inflammation)
5. Obstruction of fluid clearance in the lymphatic system
6. Changes in the water-retaining properties of the tissues themselves.

There are many types of edema:
Types include:

1. Peripheral edema: This affects the feet, ankles, legs, hands, and arms. Symptoms include swelling, puffiness, and difficulty moving certain parts of the body.

2. Pulmonary edema: This occurs when excess fluid collects in the lungs, making breathing difficult. This can result from congestive heart failure or acute lung injury. It is a serious condition, it can be a medical emergency, and it can lead to respiratory failure and death.

3. Cerebral edema: This occurs in the brain. It can happen for a range of reasons, many of which are potentially life threatening. Symptoms include:
headache
neck pain or stiffness
whole or partial vision loss
changes in consciousness or mental state
nausea
vomiting
dizziness

4. Macular edema: This is a serious complication of diabetic retinopathy. Swelling occurs in the macula, which is the part of the eye that enables detailed, central vision. The person may notice changes to their central vision and how they see colors.

5. Pitting edema: With this type, which can occur in peripheral edema, pressure applied to the skin leaves an indent or pit in the skin.

6. Periorbital edema: This refers to inflammation and puffiness around the eye or eyes. The puffiness is due to fluid buildup and is usually temporary.

Edema can occur in other locations as well, but those mentioned above are the most common.