Most common questions used to investigate
Do you leave your car parked outside?
Do you live in an area that has acid rain?
Do you live near the coast?
Do you wash your car yourself?
Common conclusions
Car paint is designed specifically to block out damage caused by the sun, but after continued exposure to the blazing hot sun, the paint could not counter the effects anymore, thus causing the paint to fade.
If you live in a city that has quite a lot of air pollution then it is almost certain the the pH factor of the rainwater there tilts more towards the acidic side of the spectrum. If you do not have a garage that can shield your car from acid rain, you should at least put a tarp or a car cover over it. If it has been raining in the past couple of days in your area, make it a habit to give your car a thorough car washing
Saltwater in the air can wreak havoc on your car's paint. Not only will the sea breeze make your car paint dull, it will also cause serious corrosion. If this is the case with you, park your car inside your garage if you have one, or cover it with a thick cover to protect your car from the sea breeze. It will also be a good idea to give your car a good waxing every so often to give its paint another layer of protection.
You might be washing your car the wrong way. You might be using brushes that have bristles that are too hard, this leaves a lot of scratches on the clear coat of the paint, making it dull. It gets worse if you use dishwashing detergent, this is too harsh and could strip away the clear coat altogether. If you will be washing your car yourself, invest in a small pressurized power washer, some microfiber towels, real carwash soap, car paint polish, and wax. You will be adding an hour or so to your usual car washing duty, but the results will be so worth it.
References
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