I'm sure there was a discussion some time ago regarding nausea in particular for pax and crew based at the rear of the plane. If I recall correctly, it was deduced that in the cruise the rear section of the aircraft had a tendency to oscillate slightly in a figure of eight motion.

(caveat, apologies for any technical inaccuracies - non-aviation professional here).

Wasn't it put down to a software glitch at the time, which caused aircraft to yaw?

Easy way of measuring the humidity is to bring on board a hygrometer and see for yourself. Some aircon shops or music shops (excessive dryness damages pianos) sell them. Should be about £10-20. The device is non-powered. Seems pretty amazing that this can be such an issue for so long with no data available.

Could cabin pressure also be involved?

IIRC when the Tristar entered RAF service in the 80s, there was an issue with cabin aie being too dry. Initially the aircraft had had humidifiers fitted; however, the original owners BA found these unnecessary and removed them to save weight. 300 pax provided enough humidity simply by breathing.
However, when the same aircraft was flying 10 hour sectors with only 3 or 4 onboard (I don't know how many crew the RAF used on them) the air was a lot drier.
The only relevance of my post is this: yes, some airliners have in the past had cabin humidifiers, but as to whether Boeing ever fitted them I have no idea.

From my experience

Hydration: nasal spray called "Sterimar" which is a salt water spray (no drugs) is very good for general hydration and unblocking of nasal passages.

Colds: Sterimar is one of only three things I have found to help reduce the time a cold blocks you up. The other two being Olbas Oil (which causes irritation if used too much, so be careful) and a Steroid given to me by an AME once. Not recommended for general use and his prescription was controversial.

Eye drops: You can get a brand of lubricating eye drops called "Blink" which are designed for contact lens wearers. The great power of these is that they come in single dose containers, about 30 to a pack. They are easy to carry airside and do not have the disadvantage of having to be chucked away after a set time due to bacterial build up. I tend to carry one or two doses (5ml ish) in my pocket for night flights and early mornings! They also help if you have allergies - sometimes when I rub my eyes (I know I shouldn't) they get irritated - Blink helps clear the irritation, although this is not what they are for. I don't use them often, but they are refreshing and helpful especially on long flights.

B777
 

I have been on the B772 for like 2 years and I aint never heard of anyone nose bleeding ......

Anyone know what the seating config on BA & KLM is?ie how many pax do they carry on the 777?

Makes me sneeze more than usual. Never had a nose bleed though. I think some sort of vertical climb in a fighter might do that, not a B777!

Cosmic radiation has been measured for years and never done anyone much harm. Given the lifestyle of most jet pilots I reckon the subsequent thrashing in the bar is more harmful to the body than any high altitude cosmic stuff. Droopy nose drivers were tested for years and dispite heavy exposure to the stuff they suffered no ill effects (not sure how it effected their offspring though!).

Generally I find the sneezing stops if I drink plenty of water in the cruise. I've found the quantitiy of water I need to keep sufficiently hydrated on the 777 is greater than previous types.

I did a little reading on this at the Boeing website, where they have a Cabin Air Systems page. Their Cabin Air Environment PDF document there has a lot of detail about the issues and how they try to tackle them.
One of their claims for the 787 is that the composite construction will allow higher relative humidity in the cabin, because it is stronger and less susceptible to corrosion. We'll see. :hmm:

By way of contrast, a relative humidity in the low 20s was the cause of complaints in the office I work in, also in winter: I had dry eye problems (with contacts or specs), some folks developed eczema and other skin problems. The 4% figure on the flight deck, quoted earlier in this thread, is one I've seen elsewhere too, which I don't think I'd like. Quoting that Boeing document again:

Cabin Humidifiers
 

IIRC, back in the early days of jet travel, one of distinctions between the British VC10 series and the American B707/DC8s was that the VC10 was claimed to be more pax. friendly, partly because it had humidifiers fitted.

Anecdotal evidence is that in recent times the remaining VC10s -- operated now solely under the banner of Crab Air -- have a well known "issue", particularly in some seats, of condensation dripping on your on head:bored: That suggests they still have the humidifiers fitted, but the higher moisture levels do have a downside.

As to the nosebleeds, I've checked my experiences and although there does seem to be some correlation between nosebleeds and 772 sectors in comparison to other types (774/340), I couldn't claim it to be statistically significant.

I fly one of the largest 777 fleets in the world (get it) and i have NEVER heard of any such thing on my airline!!! its specific only to BA i guess cuz we do really really long flights on the 777's!!!!! :ok:

Our longest stage length is BOM-JFK. 16+ hrs not uncommon and in a few cases 17+ hrs. 777ER (formerly 777IGW)

Nose bleeds have been reported to me by both my F/A's and co-pilots.

Usually does not manifest itself inflight.

Nose Bleeds, et al..
 

I've been on the aircraft since early '98, over 6000 hrs on it, have not had any reports from cabin crew or otherwise in these regards.
As for radiation hazards, I completed a study on the issue. You can drop me a note by email if you wish. In a nutshell, flying polar routes or otherwise poses no problems. All the information is from formal studies.
Safe flight..

I get nose bleeds on the 757/767 so it must be a Boeing issue! Only get it during the winter so it's related to snow and Boeings.

Well, maybe the dry air, dry house heat to dry airplane to dry hotel room, has a bit to do with it.

And Airbus' don't suffer from the same dry air/high cabin altitude because they can't fly high enough so the cabin altitude is lower vis a vis Boeing products.

Interesting info about the humidity.

When I first moved to the southwest, I found myself getting dry skin, nosebleeds, etc. from the dry air. I notice no such effects anymore..102 with 3% RH today.