I have a 5 year old Palomino Stallion that has within the last month or so started biting and nipping at me and the Palomino Mare that he has been placed with. He will not let me rub, brush, or give him treats without trying to bite me in the face. He rolls his ears back and before you know it he is nipping at you. He has always had a bad habit of nipping at my hair when I feed him but it was always playful. But he recently caught me off guard and grabbed me under the chin while I was feeding him. It did not break the skin but it scared the crap out of me at the time. Because he got me from behind while I was putting feed buckets out. He will lunge at you when he does this now. He does not do that to my husband just me. What could be wrong with him? Help!

Sounds like you need to instill some respect in that horse QUICKLY! He is progressing and could seriously hurt you if he's not put in check. He is a stallion and is out w/a mare? I don't know about you but the weather has been a bit crazy around here, I am sure the funny weather has tricked a few mares into thinking it's time to come into season. Plus, in my experience when around a stallion mares are more likely to come in anyway. But that is only a small factor and is no excuse for such aggressive behavior. You said he only does it w/you, not your husband? If he were doing it to everyone I would think there is something wrong, but since he doesn't it sounds like he's trying to exert his dominance over you. Is your husband more firm w/him?

My husband doesn't let him get the best of him. But, he keeps his distance to since he has started biting. I think he is trying to show me who is boss. I have popped him on the muzzle when he comes at me and he turns away. But, my fear is that he will catch me off guard. The weather here is really weird. It is 70 one day and then in the 30's. I know this has messed the mare's cycle up. But, there is no cause for him to do that. He has always been a good horse until just recently.

Eww, no fun. The best thing to do is STOP it and quickly before it gets any worse.

1 method: I really like this one for youngsters and horses just starting to nip/bite, but not for the experienced old gnawers.
Stand in front of your horse. Your horse nips at you or puts his mouth on you- immediately give him a good hard kick to his cannon bone (front of his shin). Popping him on the head/jaw/nose will ONLY make him headshy and/or faster at biting you. Kicking him in the leg will keep from the headshyness, and also he cannot see it coming so it will really confuse him and after about the 5-6th time, he will reach out, stop, and put his head down trying to look at his legs. He will eventually associate the pain in his legs with the nipping.

Another method: This is a John Lyons method and I like it for the more experienced biters.
Your horse bites- give him 3 seconds of H*LL!!! (minus any head-hitting) use a rope or riding whip or whatever you have handy but literally make him think you are GOING TO KILL HIM. Scare the living crap out of him for a few seconds.

And another: carry something hard, such as a metal curry comb or a rock in your hand with you into the pasture. When he comes close and you feel he is about to attempt biting, shove the hard object into his mouth, in place of a chunk of human! He should get fairly tired of biting down onto metal or rock and getting sore teeth.

Other than that, just carry a stick with you when you go into the pasture, that way if he does catch you off guard and you have nothing else to do, you can at least smack him good on the rear. Don't let him get away it even once, especially since he is a stallion.

Hope that helps!

First-Evaluate that there is a REALLY good reason for him being kept a stallion.
Gelding him is the best option.
Then realize it's not new,"He has always had a bad habit of nipping at my hair when I feed him but it was always playful. But he recently caught me off guard and grabbed me under the"[ I really want to write ARE YOU KIDDING ME !!]
Ok, So You are actually dealing with an old problem. Horses are not dogs/pets and should never be treated as such. It was fun or cute then and it really isn't now.
He needs a handler that is in charge.
You need to go back to the basics. When entering his stall/paddock... Tell him to stand up and thats exactly what needs to happen. He should stand stock still. Use a chain shank over the nose, tell him stand up and 1 quick jerk. Wait for him to move, word/jerk. Eventually you will have that same athority over him without being attached. Depending on variables will determine the time frame.
Horses learn through consistant repetition. You or any one around him must demand the same respect/responce every time. No lazy days or aw he didn't mean it.
He is an animal with animal instincts and worse a breeding age stallion.
It takes a horseman to own those safely.

i really like AQHABEEDERs' methods. im a fan of the John Lyons training and i have used his method to cure a biting horse on a few different horses. i have not had a chance to work with a stallion but a couple of these horses were down right bruetal. you need to put a sort of fear in your horse when it comes to him biting. IMO, biting is one of the worse vices a horse can have.
my little filly had a horrible biting problem and when ever she came to bite me, i would pop her on the nose, let her stand there and think about what just happended and then go back and gently rub her face all over to let her know that i dont want to hurt her. she never got headshy because i went back a rubbed her face.
if you think popping the horse in the nose will make him headshy, then dont do it. pop him somehwere else.

Awww thanks so much Dimmer_d! (feeling complemented)-

I always tried to keep from smacking them in the head/face just to be on the safe side of not growing any headshyness... of course you don't have to kick them in the shin, you can pop them on the chest/shoulder but kicking them in the shin makes it impossible for them to see when it's coming, therefore makes it alot more effective.

IF you do use a stud-chain BE CAREFUL, a stud chain can also make a Stallion angry (and you DO NOT want a Stallion angry at you) and he can be much more dangerous then, than when he was just trying to bite. I've been a stallion owner for many years, and I never use a Stud chain just as a rule of thumb: If I have to have a stud chain for control, that horse does not need to be a Stallion. I can always find a more naturally calm, obedient stud than one who needs a chain.