The main active chemical ingredient in most paint stripper is Methylene Chloride. Some other paint strippers do contain other active ingredients, but unfortunately are very slow and not as effective in removing finishes. They also can damage the condition and natural colour of many different Timber Species and some metals. A paint stripper with the active chemical called Caustic Soda would be one to stay away from, but a methylene chloride solvent based paint stripper will work fast and is safe to use on all timbers and most metals.

A good quality paint stripper can contain up to several chemicals, with the main active chemical being methylene chloride which should be at least 75% plus of the total volume of the formulation. The other chemicals are designed to accelerate the stripping process, slow the evaporation, act as thickening agents, and react with different solvent bases. So therefore it goes with out staying that these formulations of chemicals should be treated with the respect that they deserve and may pose as a health hazard to humans and animals if the manufactures instructions are ignored.

Always remember that when working with any chemically formulated paint stripper, that there are a few simple golden roles to follow. Always wear protective gloves and goggles; a face mask or respirator; old clothes and a protective apron; cover the floor with a polythene sheet and news paper and always have your work area well ventilated, or work outside.

[edit] There are number of different paint strippers available , here are just a few:

Liquid Stripper:

Normally work faster and are designed to be used in emersion stripping tanks. this method is normally adopted by commercial paint stripping companies and can be extremely costly to set up.

Gel Stripper:

Is the best for all round work, because it does not run or drip when applied to vertical surfaces. It is ideal for small to medium jobs but can become quite costly on larger projects, because most strippers will remove only 1-2 layers of coatings with each application, due to the evaporation of the chemicals contained within them.

General-purpose Stripper:

These strippers are formulated to remove practically any finish you are likely to find on furniture and architectural fittings, including water based paint and varnishes. They normally contain chemicals that will burn your skin, even the fumes they exude can be very unpleasant. However, you can work quite safely as long as you follow the golden rules above.

Varnish Stripper:

Some modern polyurethane varnishes are notoriously difficult to remove. Although a good quality general purpose paint stripper should cope with them, you can buy strippers that are made specifically for softening polyurethane coatings and traditional copal varnishes.

Safe Stripper:

If the thought of working with such potent chemicals causes you concern, you can opt to use one of the so-called "safe" strippers. The manufacturers claim that the fumes are harmless and there is no need to wear any gloves. But these paint strippers normally react comparatively slowly taking ages to achieve the desired effect. On some coatings and varnishes they will not work at all and just leave you with a mess that you will have to remove.

Metal Stripper:

These are normally specially formulated paint strippers designed to remove extremely difficult and hardened coatings from metal. They are generally used in the automotive and metal coating industries to remove two pack paints, powder coatings and speciality paints. How ever most metals coated with a general purpose paint can be easily stripped with a good quality general purpose gel paint stripper.