A recent Foundation for Consumers study has found that only one out of 13 Chinese pastry or khanom pia samples tested contained no food preservatives.
The foundation tested 13 Chinese pastries from leading bakeries at supermarkets and local markets to examine whether they contained additives.
The foundation's secretary-general Saree Aongsomwang said Thursday only one sample, taken from S&P, had no additives.
The 12 other samples contained preservatives, she added.
They were taken from Eu Leng Heng, Kru Som Song, Tae Lao Jin Seng, Khanom Ban Iyakarn, and Baan Suntiras bakeries.
The others were Tae Seng Heng, Khanom Pia Tha Dindaeng, Victory Bakery, Sing Phet, Moo Brand, Khanom Pia Bang Krabue and Gateaux House.
The amount of preservatives found in the samples was between 12.85mg and 58.77 mg per kilogramme of food, which is considered a safe amount, Ms Saree said.
A maximum of 1,000 mg of preservatives a kilogramme is allowed under law, she said.
Chinese pastries, or khanom pia, are among sweets which people buy and give to family members and friends as New Year and Chinese New Year gifts.
Monrudee Pohin, a foundation scientist, said three samples were found to contain preservatives even though the labels claimed they were additive-free.
They were found to have traces of benzoic acid, she added.
Consuming too much food containing additives can be harmful to people's health, Ms Monrudee said, adding it can lead to nausea and vomiting.
It is possible ingredients are contaminated before being used in the production processes, she noted.
She urged the foundation to examine raw ingredients to find out how products are tainted.
Ms Saree said producers who put labels with false information on their products risk violating the Food Act which carries a maximum jail term of 10 years and a fine of up to 100,000 baht.
Two tested products with Food and Drug Administration approval had no information about additives on their labels, Ms Monrudee said.
Since freshly baked products are not required by law to have labels listing what they contain, she recommended consumers ask retailers questions about the products such as what ingredients are in them and how long they can be stored.