Gray hairs are a part of science -- when the cells in the hair follicle, called melanocytes, stop injecting your hair strands with melanin, your hairs go gray. Gray hairs can be caused by genetics and even a stressful life event. While hairs typically begin to go gray somewhere between the mid-30s to 40s for most men and women, they can crop up at a younger age. But it is rare that gray hairs happen overnight -- they typically occur in small patches, which can be covered without having to dye your whole head.
Purchase an at-home color product at your local drugstore. Some products will come with highlighter pens, color markers, or touch-up combs. Choose a product that has directions with which you feel comfortable. Select a shade that is one shade darker than your natural hair color, to ensure coverage of the grays that are most persistent. Do not go more than two shades darker than your natural color.
Secure hair on each side of your head with a clip by the ears, then divide and secure hair on the back of the head with two more clips; your head of hair should be secured into four sections. If you are touching up only the gray roots, coat the ends of your hair with conditioner; this will ensure that any dripping or runaway color won't be absorbed by the rest of your hair.
Mix the dye according to the manufacturer's instructions.
Unclip the section of hair that contains the area that you want to dye, and work the bottle of dye through the desired patch of hair. Clip the section back up when you have finished with it, and repeat the dyeing process with any other sections that you wish to dye. All of the hair that is being dyed should be saturated with the dye. If you are dyeing your entire head, your hair should look completely wet. If you are dyeing just a few patches, those parts should appear completely soaked.
Allow the dye to set. Use a timer to make sure you don't leave the dye in for too long or short of a time. Most box dyes will need to sit for between 10 to 20 minutes. If you have persistent gray roots or patches, allow the dye to saturate the grays for 10 minutes longer than the rest of your hair for best results.
Rinse your hair with lukewarm water until the water runs clear through your hair and the dye is completely washed out. Apply the color-safe conditioner provided in the box. For longer-lasting results, do not shampoo your hair for two to three days.
Style hair as normal. When you have finished styling, stand under a light to assess the color. If you still have patches of gray showing, you may not have saturated the hair enough, or the box color may not be effective. Consider seeing your local hair stylist if you need stronger, more professional products. You can ask your stylist to cover individual grays instead of coloring the whole head.