AC removes water (humidity) from indoor air and robs the outer layer of the epidermis of skin. This constant loss of water and lack of replacement of water from the skin tissues below result in flaking, dry and chapped skin. Water is essential to keep the blood flowing. It performs the same function for the skin and maintains elasticity. It is important for keeping the skin’s elasticity intact. When ACs remove the water or humidity content from a room, skin starts shrivelling. Skin also becomes prone to developing creases and wrinkles. All this hastens the ageing process and there is hardly anyone in this world who would like to have skin that has aged a lot more than their actual years.

Breathing Problems
This is one of the common side effects of cold air conditioning. Effects of air conditioning on lungs are fatal.
Air conditioners are also known to circulate air-borne diseases such as Legionnaires’ disease , a potentially fatal infectious disease that produces high fever and pneumonia.

Constant Fatigue
Research shows that people who work in air-conditioned environments may experience chronic headaches and fatigue which leaves them vulnerable to contracting cold, flu and other illnesses.
Inability to Deal With Heat
Going suddenly from a cool environment to outdoor hot environment can actually induce stress. This will make you intolerant to heat or hot temperatures during summer.

Exacerbates Effects of Chronic Illness
ACs are known for increasing the symptoms of low blood pressure, arthritis, and neuritis. So if you are already suffering from illness, an air-conditioned environment will only enhance it making you more vulnerable.

Dry Skin
Air conditioner sucks out moisture from the surrounding including the skin if you are spending long hours in an air-conditioned environment. If you are not pampering your skin with the right moisturisers, your skin will soon start feeling dry.
Read more @ http://jannyhealthcare.com/?p=511

Interesting. But modern air conditioning systems are advanced enough to prevent all of these drawbacks. Of course, they cost twice or triple as much as regular ones. But believe me - from a long-term perspective, you won't regret the money spent. Also, you should consider how you clean your AC - I would recommend having https://www.airconservicingsingapore.com/chemical-wash/ at least twice a year. So your room will always be filled with fresh air without redundant elements. By the way, if you have a chronic illness, you definitely should have a talk with your doctor. In this case, AC could actually harm you.