On Monday, it was the need to curb smoking. Yesterday, we were asked to switch off our air-conditioners to save energy. And on Saturday, attention will turn to protecting the world's environment. The calendar is being rewritten, it seems, with each day highlighting a different cause. Surprisingly, many of the children in Hong Kong's schools seemed to enjoy marking International No Air-con Day yesterday. For them, it was a fun activity. Certainly, it was an effective way of making their young minds aware of two good causes - conserving energy and protecting the environment. What sort of impression it made on them, however, is open to question. Sweating it out in temperatures of more than 30 degrees Celsius is likely to remind the children how uncomfortable life would be without a cooling blast from the air-conditioner - however much electricity it uses. As some of them suggested, they were glad the activities lasted only one day. The value of dedicating a particular day of the year to a certain cause has long been recognised. But it now appears to be getting out of hand. Mother's Day has been marked for centuries. And quite rightly. Then, perhaps in the interests of sexual equality - or more likely the opportunity to sell a few more cards - Father's Day was established. But matters did not stop there. Secretaries, firefighters and nurses are among those who now have a day devoted to them - a chance for their doubtless worthy efforts to be recognised. But when it comes to promoting issues or activities, international days come into their own. Here is an opportunity to gain publicity, hold conferences, and try to persuade governments to change their policies, whether in the field of health, education, science or human rights. The United Nations must bear much responsibility for this. It observes 60 international days. The 'year' begins on February 21, with International Mother Language Day, and ends on December 18 with International Migrants Day. In between, we have everything from World Television Day to International Day for Tolerance. Perhaps the most confusing is the one which was marked on May 3 - Sun Day. But enthusiasm for international days is also found outside the UN - and the causes commemorated are not always weighty matters. September 19, for example, is International Talk Like a Pirate Day. And the last Sunday in April is Worldwide Pinhole Photography Day. There is no doubting the value of international days to focus attention on important issues. International Women's Day is a good example. But the impact of these special occasions can only be weakened with each new cause which is given its own day. Perhaps there is a need for an International Do Not Commemorate Anything Day.