If you want to use a shampoo that is free of chemicals to prevent skin irritation, you should try this homemade oatmeal shampoo.
1 cup of instant plain oatmeal
1 quart of warm water
1 cup baking soda
Put the oatmeal in a blender and grind into a fine powder.
Transfer oatmeal powder into a large container. Add the baking soda and water.
Shake vigorously until well blended.