Horror is not a genre I read or watch movies of much. But I have some thoughts about what horror is that I'll take a moment to share with you. Perhaps they will spark a thought.
Much of my thought on this stems from Camille Paglia's Sexual Personae wherein she points to the Apollonian desire for the integrity or wholeness of the person, in opposition to and fear of the Dionysian dissolution of the person in the face of nature's amoral destruction and fecundity. At bottom, horror is about the loss of identity and its reconstitution as the thing feared. It is the fear of death and transformation into the grist of nature's mill.
Get bit by a werewolf and become one yourself.
Create an artificial man out of the parts of other men.
A moron becomes brilliant through a medical procedure and realizes that it won't last and his mind will soon slip away.
Become the egg carrying womb of a space alien and watch as the baby erupts through your abdomen, sharing some of your genetic material.
Horror can mean the dissolution of the body, the mind, the moral code. It can easily be eroticised in branches of pornography dealing with dominance and submission, or the 'descent' of men into effeminacy. Obviously, this latter approach is unsuitable for your needs, but consider a story in which a person must watch their mind, or more subtly, moral code dissolve.
As with the erotic, or the thriller, or even the murder mystery, much of the power of horror comes from the anticipation; of watching the inevitable dissolution/transformation come, and discovering that no matter how much you twist and turn, you cannot escape or evade it. And beware of heroism in the protagonist. that transforms horror into tragedy. Consider District 9, where the oncoming horror of transformation into an alien prawn is muted by the heroism of the infected man. It ends on an elegiac note featuring a spark of hope that the aliens will return to 'cure' him. In the end, the creators blunted the horror.
But consider a story about some one who mutilates themselves, (physically or psychically) for a cause and in the expectation that they will be redeemed, while we as the reader know that instead, they will be betrayed and abandoned. Consider Slumdog Millionaire where the singing boys were blinded to make the gangster a few more bucks while they were young. That's horror.