How to Remove a Henna Stain
To remove henna from your skin, scrub the area with a cotton ball soaked in equal parts olive oil and salt. Let the mixture soak for 10 minutes, then wash the skin with mild soap and water. To get a henna stain out of fabric, scrub a few drops of laundry detergent into the stain using a clean toothbrush, then rinse the area with cold water.
Mix equal parts salt and olive oil in a bowl. The oil is an emulsifier, while the salt is an exfoliant, so the combination works well to get the henna off of your skin. You can use any kind of salt you wish. You could use baby oil if you don't have olive oil. Soak a cotton ball in the mixture and rub the stain with it. Vigorously scrub the stained area of your skin with the cotton ball. When the cotton ball dries out, switch to a freshly-soaked one. Keep scrubbing until the henna is gone. Leave the mixture on your skin for 10 minutes, then wash the area. Once the stained area has been scrubbed clean, thoroughly coat it with the mixture. Then, wash the area with warm water and mild soap, and rinse thoroughly. Scrub the stain with hydrogen peroxide if it persists. If you still have henna on your skin, don't despair. Soak a fresh cotton ball in hydrogen peroxide, then use it to scrub the stain. When the henna begins to rub off onto the cotton, get a new cotton ball soaked in hydrogen peroxide. Keep scrubbing until the henna is gone. Hydrogen peroxide is gentle, so it shouldn't irritate your skin. But, if your skin seems dry after using it, apply an unscented lotion to the area. Treat the stain as quickly as possible. You'll have an easier time removing the stain right after it happens than after the dye has dried and set into the fabric. If possible, treat the stain immediately. Blot the area with an old cloth or paper towel. Avoid rubbing the stain, which could make it bigger. Instead, press a soft and absorbent cloth onto the stain to soak up the excess dye. The dye will ruin the cloth, so you could use paper towels instead. Use a clean part of the cloth or towel each time you blot the fabric to prevent the stain from spreading. Scrub laundry soap or fabric cleaner into the area with a toothbrush. Put a few drops of color-safe laundry detergent onto the stain if the item can be laundered. If the item can't be laundered, spray the stain with fabric cleaner. Use a clean toothbrush to scrub the detergent or cleaner into the fabric. Continue to scrub until you don't see any dye left in the fibers of the fabric. Flush the fabric with cold water. Pour cold water over the stained fabric or place it under running water to rinse away the detergent or cleaner and dye. Don't use hot water, which could set the stain. Keep rinsing until all the bubbles and dye are gone. Apply vinegar or rubbing alcohol to the area if the stain persists. If you still see henna dye on the fabric, pour a little distilled white vinegar or rubbing alcohol onto the stain. Let it sit for up to an hour, then launder the item according to the care label. If the item is too big to launder, flush the area with cold water to remove the vinegar or alcohol. If necessary, you could scrub the fabric with the detergent or fabric cleaner again, then rinse it out with cold water. 
Mix equal parts salt and olive oil in a bowl. Soak a cotton ball in the mixture and rub the stain with it. Leave the mixture on your skin for 10 minutes, then wash the area. Scrub the stain with hydrogen peroxide if it persists. Treat the stain as quickly as possible. Blot the area with an old cloth or paper towel. Scrub laundry soap or fabric cleaner into the area with a toothbrush. Flush the fabric with cold water. Apply vinegar or rubbing alcohol to the area if the stain persists. 