Here's a very definite been there done that many times. Plus, I studied parasites at uni. Then had kids and got a crash course in applied parasitology.
We learned a lot, and developed our own fast-as-possible but foolproof and 100% effective method.
Here goes.
1) Do not believe the marketing on the containers that tells you you MUST treat every bit of fabric, clothing, toy or animal that comes into contact with the afflicted individual - it's only a ploy to sell you more of the stuff, and to distract you from your real objective be exhausting you so much you have no energy to direct where it will do the most good.
In other words, forget about bedding, soft toys, the pets (you CAN'T catch lice from a different species - I'd be looking for a new vet, or checking to see if he has shares in nit shampoo companies).
2) Nits and lice NEED body heat from A HUMAN to stay alive. An egg (nit) more than an inch away from the scalp will be dead.
To completely eliminate nits/lice from anything inanimate - leave whatever-it-is in a cold laundry for a few days. Put hats, hairbrushes, hair scrunchies & combs IN THE FREEZER OVERNIGHT. Do not share hats, hairbrushes or combs. Make sure your child knows to avoid playing dress-ups at school if there's an epidemic. Remind the school of the risk if there's an epidemic and suggest the dress-ups, or at least the hats, are put away for a while. Nothing more needs to be done, these beasts really are VERY dependent.
HERE'S WHAT TO DO - (when you're practised you can do it all in half an hour)
easy child is discovered to have nits or lice. Begin treatment immediately.
1) Get some nit shampoo. If you don't want to use anything pesticide, then use the conditioner method (or the mayonnaise - here, it will be the oil emulsion that is helping).
2) Wash the kid's hair, preferably in the bathtub. Make sure the room is warm, comfortable (with a low stool for you to sit on) and entertaining. Use the nit shampoo according to directions. by the way, the child should be naked, and you should have your own hair in a shower cap. The child's clothes - put them into the cold metal laundry tub. Forget about them for a few days, then cold wash and dry on the clothes line outdoors if you can.
3) Put plenty of conditioner (or mayonnaise) in the kid's hair. Comb it through with a wide tooth comb then when it seems tangle-free, comb through with a nit comb (fine tooth comb, either plastic or with those round metal teeth that seem to have no space at all in between). Be patient with this - if it seems to tangle, reach for the wide tooth comb.
4) Comb through the hair, detangling first then fine-tooth comb until you've covered every part of the head. Every few passes of the comb, rinse the comb in the bathwater. If the child by now is out of the bath, have the child sit in front of the TV with a favourite movie on while you do this, and use a bowl of water to rinse the comb in. Also keep a kitchen cloth handy to wipe the comb on, and keep the cloth in the bowl of water.
5) You've done the whole head? Sorry, not quite done yet. Time to change combing direction - use the wide tooth comb to flip the hair forward, or back, or sideways - whichever you have not yet done - and repeat (3) and (4).
6) Send the kid to get dressed. If you used mayonnaise, send the kid to wash hair, and then get dressed.
7) And now for clothing - put in the laundry, any shirt you and the child were wearing while you were doing this. If you're really concerned, change the pillowcases. Don't bother changing anything else unless you just got the kid out of bed. Usually though, the child hasn't been in bed in recent minutes because we tend to find nits in daylight after the child has been up for a while. A bed which hasn't been slept in or lain on by an infected child for a few hours is unlikely to reinfect.
8) Put in the freezer any hair brush or other hair implement/item/adornment likely to have been used by the child in the last 24 hours. Leave them in the freezer for six hours at least.
And check everyone else. Including yourself. Check hair in sunlight for best detection. Even a bright light almost directly on the head is not as good as sunlight. I don't know why.
The method above is also a good way to check if you have lice - simply examine the fine tooth comb yourself after each pass.
AND NOW THE VERY IMPORTANT LAST STEP -
Do it all again in six or seven days. No longer. If you find any lice, then again repeat, in another six or seven days. Keep repeating every six or seven days until you get a clear run.
The reason you repeat, is because the eggs don't all get killed. Conditioner and mayonnaise will not do a thing to the eggs, any live eggs will hatch and the babies grow up to be mummy and daddy lice by about 8 days. It is a really good idea to get them OFF the head BEFORE they become mummy and daddy lice and lay more eggs.
If you are following this scrupulously, and you keep finding them, then look around - the kid is getting reinfected somehow, from someone else. It's NOT going to be your lack of care, unless you've been a bit too slap-dash about it. You will know. The most likely place for reinfection is school, especially in younger grades, and some family relatives who won't accept that these things exist.
easy child had nits for months and months and I didn't recognise what they were, until the class teacher pointed it out to me. She must have passed them on to so many kids, I was mortified. And of course, by then she had passed them to everyone in our family, we had a big job cleaning them all up.
And that is another thing - if you need to treat everyone in the same family, do it all together. You may need extra combs and extra bowls of water and all end up looking like chimps in the jungle grooming each other in a circle, but you do whatever works.
I've already mentioned other precautions.
The method above works really well. We stopped fussing about all the extra stuff and still had 100% success rate.
I remember difficult child 3's last case of nits - we were on holiday, had been for a week. He must have picked them up at school, nobody else in the family had them. He also had a big scab on his scalp which he'd been picking obsessively at, so we'd been dabbing pure ti-tree oil onto the scab. When we found the lice (and nits) it was clear that ti-tree oil, so often sold in 'herbal nit treatments', was not doing a darn thing, they must have been drinking it for a week already.
We found the nits just as we were shopping prior to going on a long drive and a picnic. We bought a bottle of treatment (in this case a foam treatment which I found easy to use) and went straight back to our unit. No bathtub, so I washed difficult child 3's hair in the shower and smothered his scalp in the foam then sat him down to watch the cartoon channel on the cable TV. I had a cup of coffee while I waited for the time period, put my hair up in the cheap plastic hotel shower cap and began to comb. It took me 15 minutes to thoroughly comb out his hair. Meanwhile husband had packed the picnic basket, organised everything else and as soon as I put down the combs and tossed difficult child 3's shirt and towels onto the bathroom floor, we headed off for our (slightly delayed) picnic.
Holiday - not spoiled in the slightest. As we had lunch in the park, I used the wonderful Queensland sunshine to check everybody else a bit more carefully.
Sometimes when your kid gets nits and you took a while to notice, he/she could have passed them on to an elderly relative who simply has never experienced them. YOU clear them up, but elderly relative now harbours an independent colony of them just waiting for another cuddle from difficult child. Trying to check an elderly relative, let alone persuade them to be treated, is difficult. If you've already practised on your child then use your new skills to treat the relative. If they won't comply, limit the physical contact or find some other tactful way to suggest a visit to the hairdresser - "a trim would make you look even younger. gran."
Anyway, hope this helps.
And don't use kero - it's not been advised for 50 years. It's a worse chemical than many other toxic pesticides, and if you have a smoker in the house it can be dangerous. I'm currently reading a biography of a scientist in the 1830s, and the doctor has advised as a routine treatment for a baby, things like calomel (a mercury compound), antimony (twice daily) and ammonium carbonate to help the baby sleep at night. After that, kerosene on a shaved head to cure nits seems perfectly acceptable.
I hope you can sort this out with little fuss.
It happens to the best of us, don't fret. As the child gets older, it happens far less.
Marg