When students at a San Antonio, Texas, school went on a field trip this week, parent Christy Riggs wanted her daughter to bring sunscreen along to protect her from over six hours in the sun. To her dismay, the North East Independent School District has a ban restricting students from bringing sunscreen to school or on field trips because it is considered a toxic substance.

"The school wants us to lather our kids up in sunscreen before school, but when they're outside all day or swimming, they need to be reapplying every couple hours," Riggs told ABC News.

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Riggs' daughter got a sunburn after the field trip, her mother says, something she has been able to avoid over the years because of consistent sunscreen use.

"Our family has very pale skin, and my father actually passed away from skin cancer earlier this year," Riggs said. "What sort of message is the school sending when they tell us to leave sunscreen at home?"

School district spokeswoman Aubrey Chancellor said allergic reactions to sunscreen are one of the numerous reasons the district does not allow sunblock in its 72 schools.

"We don't want students sharing sunscreen," Chancellor said. "If students get it in their eyes or react badly to the sunscreen it can be quite serious."

Chancellor said the district treats sunscreen like a medicine and that children need a doctor's note to have it at school.

"If there are extenuating circumstances," she said, "students are welcome to keep sunscreen in the nurse's office and go there to reapply."

Parents, including Riggs, have expressed frustration at the policy. "We want to teach our children to eat healthier, yet we have them outside and let them burn," Riggs said.

Indeed, studies show that if children have one bad burn, their chances of getting melanoma double, prompting Riggs to be all the more careful.

"I'm not saying all children should be required to bring sunscreen," Riggs said. "But skin cancer is on the rise and reapplying at school shouldn't be an issue."

District officials review school policies yearly, and spokeswoman Chancellor said there is a chance they will revise their ban on sunscreen. Until then, students will have to come lathered in sunscreen and will not be allowed to reapply unless they have a doctor's note.