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It can thicken up as it sets, so you may need to moisten the mixture. Slowly add more water or your chosen liquid until the henna is back to a smooth, mud-like consistency. Henna will stain anything that it comes into contact with, including your skin, so it’s important to make sure you’re covered. Applying petroleum jelly or another thick cream or balm along your hairline, ears, and necks will prevent the henna from staining your skin. Make sure to wear rubber, latex, or some other type of protective gloves while you’re applying the mixture to your hair.  Wear clothes that you don’t mind getting stained when you apply the henna because drips or spills may happen, and you won’t be able to get the color out of your clothing. It’s a good idea to apply your henna in the shower or bathtub, so you don’t have worry about getting it on your furniture, carpeting, or other surfaces. If you do get henna on your skin, wipe it away immediately. The longer that it sits on your skin, the worse the stain will be. It can take several days for a henna to fade from the skin. Henna is thicker than other types of hair dye, so it can be difficult to ensure that you spread it all over your head. Working with individual sections of hair makes it easier to saturate all of it. Gather all of your hair and clip it up, leaving only a small section, approximately 1-inch wide, to start with. You want to really saturate the hair with the henna mixture, so don’t be afraid of applying too much. Take your time to ensure that you cover every strand with the henna too.  Do your best to avoid getting henna on the sections that you’re not working on at the moment. Henna can tangle your hair very easily, which may make it harder to work with the other sections later. You can use a piping bag or squeeze bottle to apply the henna if you're having trouble controlling where it goes, but it's usually easier to use your fingers so you can really work it into your hair.  For total coverage, apply the henna all the way up to your scalp. You may notice some slight staining, but it typically fades with a couple of hair washes.  Because the thickness of henna can make it difficult to apply, you may want to ask a friend to help you color your hair, especially if you have long or extremely thick hair. Henna is more effective when it’s kept warm, so covering the mixture as it sits on your head helps your red color turn out more vibrant. Check the henna package instructions to see how long you should leave it on your hair. It can take anywhere from one to six hours, but the longer that you leave it on, the deeper your red will be.  Letting your henna sit on your hair for three to four hours will usually give you a nice, rich red color. If your natural color is dark, you may want to leave the henna on for six hours to ensure that you get a noticeable red hue.

Summary:
Check your henna mixture before application. Protect yourself from stains. Divide your hair into sections. Apply the henna to each section of your hair. Cover your hair with a plastic cap or wrap.