Example of a longan tree where the fruit is usually harvested once a yearThe size of the ones grown in Samut Sakhon are large, the fruit is sweet and usually you would not develop cough unless you have eaten lots of it. If you are already coughing, then you need to stay away from longan as this fruit, as delicious as it is would aggregate coughing.
If you love longan (pronounced as lamyai ลำไย in Thai), you would be be able to find the most delicious longan in Thailand, specially those grown in the province of Samut Sakhon: Longan is one of my favourite fruits and I look forward to eating it each year. Longan session falls around end November to early February of each year. The usual session is once a year. However through advancement in agricultural technology, it is sometimes available twice a year. The taste is very different if you compare to the longan that are shipped to Malaysia and Singapore from Thailand or those grown in Malaysia (in Malaysia longan is known as “mata kucing”). Those shipped overseas tend to cause cough compared to the ones bought from Thailand directly. I was told is because prior to being shipped out, they had to add chemicals in order to avoid the fruit from spoiling or rotting. If you buy from the district of Ban Phaeo, the longans are fresh and the use of chemicals is minimal. Sometimes overseas visitors who have too much of longans may develop cough because the nature of the fruit would trigger cough, just as too much of durians would trigger sore throat.