Wait five minutes. (Read something or whistle the Lone Ranger's anthem.) Rinse out the juice, then shampoo as you usually do.
The lemon juice's citric acid helps to slough off dead skin cells and kill the bacteria that clogs oil glands, allowing the release of subcutaneous scalp oils that will stop the itching.
Keep an eye or two on your skin which might be caused by stress or anxiety. You'll feel better giving yourself a Lemon Aid.
Hand Sanitizers are Not a Substitute for Good Old-Fashioned Scrubbing
Long term care facilities which depend on these hand sanitizers report more cases of a norovirus, a common malady in such residences. Those that cause flu and colds as well as most bacterial infections, don't work effectively against this "stomach bug." Such maladies can lead to colon inflammation.
The upshot is after using the bathroom or touching another individual, give your hands a super soaping before eating or handling food.