Accidental formaldehyde intake or its mal use as a food additive for preservative purposes may lead to deleterious effects on almost all body systems.
After daily oral administration of 80 mg/kg formaldehyde for 4 weeks, many histological gastric changes were observed. These results are in agreement with those obtained by previous researchers . In contrast, others  did not observe any adverse effect in the stomach of dogs and rats after oral administration of formaldehyde at doses up to 150 mg/kg body weight/day in drinking water for a period of 13 weeks. This discrepancy can be explained by the differences in the strains of animals used .
The present study revealed that there was highly significant increase in the thickness of the lining epithelium of the fore-stomach and glandular-stomach associated with hyperplasia. The scanned luminal surface of the fore-stomach revealed numerous keratin scale. These findings are in agreement with those of previous studies [1,22] in which the effects were attributed to the irritating, corrosive, and toxic effects of formalin.
This study showed inflammatory cellular infiltration and dilated blood vessels in the mucosa of the fore-stomach and the glandular-stomach as well as multiple erosions and edematous spaces in the glandular-stomach. Necrotic debris was detected by a scanning electron microscope. Similar results were found by some investigators  in their study on gastric mucosa. All of the previous pathological observations indicate the occurrence of gastritis as reported by various authors [24,25]. Other investigators  reported that formaldehyde ingestion induces corrosive damage and hemorrhage of the gastrointestinal tract, which depends on the duration of contact. Furthermore, the local gastrointestinal effects, including ulcers and perforation, can be attributed to the necrotic effects of formaldehyde on the mucus membrane . Moreover, some researchers  found that, in a case study of attempted suicide, ingestion of formalin causes disorders in the oral cavity and the gastrointestinal tract. The stomach shows the most severe damage in such cases because contact of formalin with the gastric mucosa is longer than in the other parts of the gastrointestinal tract. Gastric ulcers and mild hemorrhage are frequently seen. They added that ingestion of formalin could lead to peritonitis without perforation because of gastric wall inflammation. The cicatricle stricture of the stomach tends to be a major problem in the late phase of formalin ingestion.
The present study revealed cytoplasmic vacuolation of gastric gland cells accompanied by hyperplasia of the gastric epithelial cells. Previous studies  mentioned that these degenerative and proliferative gastric changes are most probably related to the cytotoxic properties of formaldehyde. Other studies  reported regenerative activity in the glandular stomach and increase in the number of mucus cells in deep gastric pits of the fundic mucosa of rat provided 5% formalin in their drinking water. Other researchers  reported that the highest tumor response should be expected at sites with the highest cell proliferation activity.
As regards the Feulgen reaction for DNA used in this study, there was a significant decrease in the reaction in the experimental group. This indicates a decrease in the DNA content of the gastric cell nuclei. This result is in disagreement with the results of a previous study , which showed no evidence of carcinogenicity of formaldehyde even after 2 years of oral administration. However this result is in accordance with that of another study , in which nuclear changes in the stomach, duodenum, ileum, and colon were found and the strongest genotoxic effect was observed in the stomach. These data suggested that formaldehyde not only causes nuclear damage at the site of application but also at distant sites. Some authors  reported a significant decrease in the nuclear DNA content of the testis and prostate. Other authors  assumed that a threshold for carcinogenicity exists after exposure by inhalation and oral administration. The rates of gastric tumor incidences in male rat administered 1500 mg/l were 4% in the original study  and increased to 14% in the re-evaluation study . The carcinogenicity of formaldehyde may result from its ability to induce DNA–protein cross-links . Some researchers  suggested that formaldehyde is genotoxic as a result of its ability to arrest DNA replication. They added that, although DNA–protein cross?links could be removed and DNA could be repaired, failure to remove the blockage before cell division or incomplete repair could cause cell death or a mutation.
On the basis of the previous data, this study concluded that oral formaldehyde intake has deleterious effects on albino rat stomach in the form of irritating and regenerative effects as well as DNA damage that may be precancerous.
Therefore, it is recommended to prohibit the mal use of formaldehyde as a food additive, and appropriate control measures or alternative additives should be used.
There is no conflict of interest to declare.
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