Why is SLS poison for my scalp but not my skin?

[Roseate]

My hair, and especially my scalp, has been so happy since I stopped using sulfates. My scalp was always some combination of scaly, flaky, crusty and scabby when using SLS shampoo, and it still has a reaction after just one wash, no matter how diluted.

But, I've used SLS-containing body and face washes with no problem at all, though I do sometimes get flakes on my widow's peak if I let a SLS-containing wash get on my hairline. My favorite Tom's toothpaste has SLS. (A quick check of my shower in fact shows no SLS at this particular time, but my skin has always been generally happy other than my scalp, and I've definitely used it in the past. Cetaphil has it.)

What gives? Why does the skin on my scalp hate this ingredient with a burning fiery passion, while one centimeter away, my face likes it just fine? Anyone else have a similar experience?

[Pegasus Marsters]

It's possible to have localised skin sensitivities. For example I can use products on my body that my facial skin would freak over. I have one patch of skin on the back of my neck that is very sensitive and burns if I get certain products on it, even if the rest of my skin is fine with the products. There's nothing visible on that patch, it just burns.

[Copasetic]

I have had a similar experience. SLS products are fine for me, except when it comes to my back. They really irritate the skin on my back, and give me a rash. I finally just gave them up entirely.

[RancheroTheBee]

I can put pretty much anything on my scalp, no problem. But if I leave the house without SPF30 sunscreen, the Sun Gods claw at my face. Oh, and I can't use at least half the face washes on the market, or my skin turns red for several months. So, I feel your pain.