Do you want a dramatic change? For the best results with boxed home hair color kits, stick with hues that are no more than two shades lighter or darker than your current color. Anything more dramatic warrants a trip to the salon.
Are you going lighter? You'll probably need a permanent hair color. These strip the natural color out of your hair, replace it with a completely different color, and never wash out.
Do you just want to cover some grays? For this, you don't need to go all-out with a permanent hair dye. Gentler demi- or semi-permanent dyes will blend away the gray without damaging your hair. They'll wash out eventually, though (within four to 28 shampoos, depending on the formula).
Are your roots showing? Root touch-up kits can buy you an extra two to three weeks between hair colorings. To instantly hide roots, try a temporary root concealer. These come in powder, spray, crayon or marker form, and they'll wash out with your next shampoo.
Is your hair damaged? For mildly damaged hair, gentler semi- or demi-permanent hair colors are your best bet. For really fried hair (or to fix a bad dye job), go to a pro.
Don't skip the strand test. Some hair types process color faster than others. Damaged and color-processed hair can take half the processing time of healthy, uncolored hair. The instructions in the box will tell you how to do a strand test to judge your processing time.
Always do the patch test -- even if you've used the product for years. Some users have suffered allergic reactions when their favorite hair colors changed formulas, and sometimes even when they didn't. Follow the instructions in the box to check for skin reactions before you begin.
Have you had allergic reactions to hair color in the past? Paraphenylenediamine (PPD) is a common culprit. This chemical is found in most hair color products, both cheap and expensive. "Many people are allergic to it," Cleveland Clinic dermatologist Melissa Piliang says. "Any scalp redness, irritation, itching, scaling, flaking or blisters should raise concern," and if symptoms are severe or last more than two days, you should see a doctor. Some PPD-free hair colors are available; check the ingredients to be sure.
Do you have a sensitive nose? Most permanent hair dyes have a strong odor, but some use fragrance to mask it. Ammonia-free semi- and semi-permanent formulas generally don't smell as bad.
Don't trust the model on the front of the box. Instead, match your current hair color to the chart on the side of the box to see what your results will be.
Male or female? It doesn't matter. Some hair dyes are marketed as "just for men," but in reality, men and women can use exactly the same hair dyes to color the hair on their heads (although some special products are available to dye men's facial hair).
Condition, condition, condition. All permanent hair colors use a process that involves bleaching or lifting the current color and then adding the color that you want, all of which can dry and damage your hair. Experts say you should condition color-treated hair after every shampoo and do a deep condition once a week.