It is common when traveling to areas with large numbers of insects, mosquitoes etc. to apply insect repellent. In fact, it is often advised; especially in areas where diseases such as typhus and malaria are prominent.
The key ingredient of many insect repellents seems to be a N,N-Diethyl-meta-toluamide, known mainly through its acronym, DEET. Although considered generally safe when used responsibly, it is considered ‘slightly toxic', and does cause damage to freshwater fish. Additionally, some regular uses of insect repellents with high concentrations of DEET (70% and above) were shown to have various negative side effects such as irritation and some pains; some effects can be more serious. Nevertheless, as it is a toxic substance, it requires careful treatment of usage as well as disposal.
As travellers we have to be responsible in using these products. We should remember to read instructions on the repellents before using them, especially for repellents with high concentrations of the chemical. These should generally be washed off with soap when no longer needed, and should not be used excessively. Care should be also taken to ensure that it does not escape into the environment and harm animals.
If a traveler wishes to reduce the potential risk, they may use other alternatives, such as organic repellents, however, it is always important to check on exactly what we are using. Assuming something is completely safe purely because it is labelled ‘organic' may also have its consequences. This may apply beyond just repellents, various products have effects we do not realise or simply do not read on the labels.
As travelers we are exposed to many products that may use chemicals whose effects we are totally unaware of, such as the repellents, sun screens and so on. Nowadays, the small print on products are almost never read, and we remain ignorant of potential side effects while the information is literally right under our noses. As a traveler we have a greater responsibility to know what exactly we are using to avoid carrying around hazardous material! Don't just take things for granted!