How long can I leave henna in for?

[RancheroTheBee]

I have been Googling this for almost an hour. I can't find any information on the maximum amount of time for leaving henna in. I'm waking up tomorrow at 9:00 to wash it out, because I assume that "overnight" means 8 hours.

Help?

[Jeni]

There are people here who sleep with henna on (I believe). I use to leave my henna/cassia on for 6 hours and no problems.

[3azza]

I know that 3-4 hours is enough time to get good dye release, i leave mine for three hours and i get good colour. I know lots of people who leave it overnight and wash it the next day and that's fine as long as you're able to sleep with it.

[Heidi_234]

Until it dries I suppose. Dry henna can't do any good, but make rinsing out little more difficult (I guess). People did overnights and it was all good. If you starting feel unwell while the henna is on your head, then you should rinse it out. Other than that, 8 hours would give you deep enough stain for sure.

[Gothic Lolita]

I believe you can leave it on as long as you wish, simply wrap your head with saran wrap or something alike to make sure it doesn't dry out.
Nightshade did some staining experiments and found out that henna still stains after 52 hours. That's nice o know but believe me, you don't want to run around with the mud that long. Your head will get pretty heavy after a while. I'd say apply in the evening and the sleep with it. That will give you a really deep stain and wonderful conditioning without having it on the whole day.

[cleanbug]

I have researched henna on the Henna for Hair site. After 4 hrs, you will have plenty of stain on your hair.
However, you can leave it on for longer if you like. I sleep in it sometimes so i don't have to walk around with it on half the day. It will continue to make your hair darker the longer you have it on (especially if you are overlapping previously hennae'd hair).
I like my hair dark so i don't mind this.
All the best.

[Nightshade]

I believe you can leave it on as long as you wish, simply wrap your head with saran wrap or something alike to make sure it doesn't dry out.
Nightshade did some staining experiments and found out that henna still stains after 52 hours. That's nice o know but believe me, you don't want to run around with the mud that long. Your head will get pretty heavy after a while. I'd say apply in the evening and the sleep with it. That will give you a really deep stain and wonderful conditioning without having it on the whole day.

Pretty much exactly what I was going to say :p That and agreeing that you could in theory leave it on until it dried out.

In the experiment I did on dye demise (http://forums.longhaircommunity.com/showpost.php?p=48729&postcount=23)I was still getting good stain at 24 hours, but it started to taper off by 48, and was very faint at 52.

More than 8 hours is probably unnecessary, and I think you'll get a good 90% of the color and conditioning you want in 4-5 tops.

[RancheroTheBee]

Awesome! Thanks everyone. I just wanted to make sure I wasn't going to do any damage by leaving it in too long, and I tend to sleep for +11 hours if I can get away with it. :p I guess from now on, henna can just be a daytime affair.