In the most literal sense, yes, candles are bad for the environment because they release an assortment of pollutants when they are burned, just like anything else, as combustion generates an assortment of chemical compounds. However, open fireplaces and cars are much more of a concern, along with unclean power plants, dirty manufacturing processes, and a host of other environmental problems. Although it is an excellent idea to be environmentally conscious and to make sound environmental choices, candles should probably not be at the top of your list for reform.
That said, some candles are worse than others, and while you do not need to stop burning them altogether, you might want to think about more environmentally sound varieties, like those made from beeswax, soy, or other vegetable products, rather than traditional paraffin ones. With a growing awareness of environmental issues, several manufacturers have begun to focus on providing “green” alternatives which are good for the Earth, making environmentally sound choices very easy for consumers.
Burning candles can be bad for the environment in a number of ways. The components of the candle are the primary source of environmental problems. Paraffin candles, for example, produce a number of byproducts when they are burned, including greenhouse gases like carbon dioxide. Paraffin is also a petroleum product, making it a nonrenewable resource and adding to pollution through oil spills and other issues associated with the oil extraction process. Candles also produce soot, a particulate material which can be a lung irritant, and scented or treated varieties may release harmful chemical compounds when they are burned.
The wick is also an issue. Some candles are made with wicks that have additives like lead and zinc, which can release harmful gases when they are burned. While lead wicks are banned in some parts of the world, these bans are hard to enforce, and it is relatively easy to find them, unfortunately. You may also want to consider packaging; many candles, for example, are packaged in plastics that are thrown away, rather than paper or biodegradable wrapping.
No candle is going to be exempt from causing at least a small amount of environmental damage, but on a global scale, a few used to brighten a dreary evening are not going to make a major difference, especially if you choose more environmentally friendly materials and packaging. A soy wax candle burned in a recycled metal tin, for example, is a better choice than paraffin candles individually wrapped in plastic packaging.