Everything is JKR's, I just have allergies.
"ACHOO!" Snape sneezed violently, turning away from the cauldron he was stirring. "Damn it all!" He grumbled. "That's the fourth potion I've ruined today!" Snape hadn't missed a single day of teaching in the past twenty-five years, for sickness at least. During the war, after he'd killed Dumbledore and days when he was Headmaster... But that was a different story. He'd had to miss some days in order to accomplish the great plan of Dumbledore's. Well, at least it had worked. Still... It had been a very long time since he'd had even a sniffle. And for someone who lived nearly 24/7 in the drafty dungeons, that was quite a feat.
He paused in his stirring for a moment, running through cold and flu symptoms in his head. Runny nose and sneezing, check. Although he was pretty sure the runny nose had been brought on by his violent sneezes. Cough and/or sore throat, nope. Fever, no. Headache, no. It had been a lovely, quiet Saturday in the dungeons with no dunderheaded students around to give him a headache. Upset stomach, no. Why on earth would he be arbitrarily overcome with violent sneezes?
He shook his head and turned back to the potion he had sneezed on. Blast! He'd have to re-do it for the fourth time today. It was such a simple potion too, just burn salve for Madam Pomfrey. If word ever got out that he, Severus Snape, the most powerful Potions Master of the age, had had to re-make burn salve four times in one day... He'd never hear the end of that one. And as he was still hearing about Potter's spilling of his darkest secrets at the Final Battle, it's a wonder he wouldn't die of embarrassment on the spot!
With a deep sigh, he began to clear up the area he was working in. He'd take a break and go up for dinner in the Great Hall before starting again. He took his seat silently as usual next to Professor Granger. When he had turned down the post of Headmaster when Hogwarts re-opened after the Final Battle, Headmistress McGonagal had appointed Hermione as the new Transfiguration professor.
Snape didn't actually mind that particular addition to the staff. She was polite and very intelligent; occasionally they had fascinating conversations at the dinner table. Their relationship never went beyond the staff table, but it had reached a point where he didn't mind speaking with her as he did most of the idiots that surrounded them. He could just talk to her, instead of spitting niceties through his teeth at the fools.
She turned to greet him after finishing her conversation with Professor Flitwick, on her other side. "Good evenin- Oh, dear, what did you do to yourself, Severus?" She exclaimed, looking slightly amused. He raised an eyebrow at her.
"What do you mean?" He asked.
"You're covered in green powder," She told him. He looked down. She was right. The finely ground green monkshood for the burn salve had settled all over him, giving his robes and hair an eerie, glowing look.
"That explains the surprised looks I received when I walked in," He mumbled to himself.
She brushed the shoulder of his typical black robes, causing a fine acidic green powder to cloud the air near his ear. "ACHOO!" He sneezed again, quickly turning away from her and raising his arm to his face in a desperate attempt to avoid making a mess. It worked, and he turned back to see her looking even more amused, trying not to laugh.
"My apologies, I can't seem to stop sneezing today," he grumbled to her. Her lips twitched, but she didn't smile, knowing how much that would aggravate him.
"It's alright, happens to the best of us," She waved away his apology. "Have you caught a cold?" She asked.
"No, I have none of the other symptoms. Just this infernal sneezing all day." He told her.
She looked thoughtful. "It is springtime, Severus. Perhaps you are allergic to something during this time of year that doesn't bother you during the other seasons."
His eyes narrowed and his brow furrowed as he thought it over. "Perhaps you are correct, Professor Granger. I don't recall ever brewing burn salve during the spring before."
She giggled. He met her eyes with his eyebrow raised. "What, pray tell, is so funny?" he demanded.
"Imagine, the most powerful Potions Master of the century is allergic to green monkshood!" She couldn't help laughing a bit, it was such a ridiculous idea. The ingredient was crucial to many of the simplest, yet most important healing potions. A Potions Master would have to deal with it on an almost daily basis.
He glared at her. She couldn't help it, she giggled again. "How many potions did you ruin today, Severus?" She asked.
"Four! It has been simply pathetic!" He complained. "And I haven't managed to complete any burn salve so that's how I'll be spending my evening as well!"
"All right, all right. Poppy does need that burn salve by tomorrow morning, so instead of you complaining all next week about not being able to get any work done, I'll come down after dinner to the dungeons and brew it for her. Seeing as how you clearly won't be able to do it until your allergies clear up," She told him kindly, laying her hand on his forearm for just a second.
"You would do that for me?" He asked. Why would anyone do that for him? He's just the snarky Bat of the Dungeons.
"Yes, of course." Hermione smiled at her friend. "That's what friends are for, and Poppy really does need the burn salve as soon as possible. I'm sure she's wondering what's taking you so long with it, she was probably expecting it by this afternoon at the latest."
Snape thought for a minute. "Well, you are definitely the most competent at potions compared to the rest of the staff. You would easily be able to accomplish the salve."
"I'll see you in the lab after dinner then," She said.
She was just finishing up the second batch of burn salve when she heard sneezing in the other room. She laughed again, thinking to herself. One of the most invincible men in the world, and he couldn't make a simple burn salve because of allergies. "Poor man," she said to herself over the mixed sounds of violent sneezing and swearing. "Perhaps I should tell him about muggle allergy medications..."