Omega-3 and Omega-6 fatty acids are both polyunsaturated fats that our bodies need in order to function.
Omega-3 Fatty Acids:
The main omega-3 fatty acids are Eicosapaentaenoic acid (EPA), docosahexanoic acid (DHA) and Alpha-linolenic acid (ALA). The first two are found in abundance in fatty fish. ALA is in plant sources such as flaxseeds, chia and walnuts.
Omega-3's have powerful anti-inflammatory properties. DHA is a major structural component of the brain and is essential for cognitive function and brain development. Omega-3's can lower triglyceride levels, reduce blood pressure and decrease the risk of heart disease.
Omega-6 Fatty Acids
The main Omega-6 fatty acids are Linolenic acid (LA) and Arachidonic Acid (AA). LA is found in all sorts of vegetable oils, including sunflower, safflower, corn and soybean. AA is found in meat, poultry and eggs.
Omega-6's help support healthy skin and hair (LA), as well as contributing to bone health by influencing calcium metabolism. They also play a role in cell membrane structure and function.
Omega-6's are both pro-inflammatory and anti-inflammatory. We need some degree of healthy inflammatory response to manage immune responses and healing.
The Balancing Act
So why are we always led to believe that Omega-6's are 'bad' for us and promote all sorts of health issues?
The key point is balance. Our bodies do need both, but in differing amounts. And currently, because of the nature of the modern diet, we have a tendency to consume far too much omega-6 and not enough omega-3. Up until about 100 years ago the omega-6 / 3 ratio was around 4:1. It is now around 20:1 (in favour of omega-6). This is due to a century of processed foods and promotion of "healthy" fats in our diets that were in fact anything but.
The Answer?
The general recommendation is to increase consumption of omega-3 fatty acids and limit that of omega-6's. In real terms this means eat fatty fish, walnuts, flax seeds and chia seeds. And keep your intake of processed foods to a minimum. Replacing refined seed oils for cooking (especially the generic all purpose "vegetable oil") with animal fats, coconut oil or olive oil is also a great help.
Sources:
The Role of Omega-3 and Omega-6 Polyunsaturated Fatty Acid Supplementation in Human Health : The Importance of Maintaining a Low Omega-6/Omega-3 Ratio for Reducing the Risk of Autoimmune Diseases, Asthma, and Allergies : The importance of omega-3 and omrga-6 fatty acids : Food Foundation