Measles vs rubella: how the two rash illnesses differ

Measles and rubella (also called German measles) are two separate viral infections that happen to share a spotty rash, which is why they are so often confused. Both are prevented by the same vaccines, both spread in coughs and sneezes, and both usually clear up in about a week.

The main differences are in how unwell you feel and in what can go wrong. The NHS describes measles as an infection that spreads very easily and can cause serious problems, including pneumonia, meningitis, blindness and seizures. Rubella is usually milder, and the NHS calls it a rare illness. Its real importance lies in pregnancy, where it can cause miscarriage or lasting problems with a baby's sight, hearing, heart or brain.

Neither can be reliably told apart by looking at the rash alone. A person with a rash and a temperature, particularly a child, needs a clinician to decide what is going on.

According to the NHS, measles usually starts with cold-like symptoms: a high temperature, a runny or blocked nose, sneezing, a cough, and red, sore, watery eyes. Small white spots may then appear inside the cheeks and on the back of the lips, usually lasting a few days. The rash follows a few days after the cold-like symptoms, starting on the face and behind the ears before spreading to the rest of the body. The spots are sometimes raised and can join together into blotchy patches, and they are not usually itchy.

Rubella often feels much less dramatic. The main symptom, according to the NHS, is a spotty rash that starts on the face or behind the ears and spreads to the neck and body, usually lasting a few days. People may also have swollen glands in the neck or behind the ears. Other possible symptoms include aching fingers, wrists or knees (especially in adults), a high temperature, a cough, sneezing, a runny nose, a headache, a sore throat and sore red eyes. Some people have no rash.

The NHS says measles can lead to serious problems if it spreads to other parts of the body, such as the lungs or brain. These include pneumonia, meningitis, blindness and seizures. They are rare, but babies and people with weakened immune systems are more at risk. A baby under 1 year old who has come into contact with someone who has measles is among the people the NHS advises to seek urgent advice.

For rubella, complications in the person who catches it are much less of a concern than the effect on a pregnancy. The NHS says rubella is very rare in pregnancy, but if it is caught then it could harm the baby, with a risk of miscarriage or serious problems after birth with sight, hearing, heart or brain. The risk is highest early in pregnancy, and the NHS says there is not thought to be a risk to the baby if rubella is caught after week 20.

Measles in pregnancy is also dangerous. The NHS lists miscarriage or stillbirth, premature birth and low birthweight as possible outcomes, and advises anyone pregnant who has been in close contact with someone with measles to get medical advice.

Both illnesses spread through the air when an infected person breathes, coughs or sneezes, and both are infectious before the rash appears, which is one reason they spread so easily in nurseries and schools.

The NHS says people with measles are infectious from when they first have symptoms, around 4 days before the rash appears, until 4 days after the rash starts. For rubella, it says the infection is spread from 1 week before symptoms start and for at least 5 days after the rash first appears. For both, the NHS advises washing hands often, using tissues, not sharing cutlery, cups, towels, clothes or bedding, and avoiding close contact with anyone who is pregnant. For measles it also advises avoiding contact with babies and people with a weakened immune system.

The NHS advises that anyone who thinks they or their child may have measles should ask for an urgent GP appointment or get help from NHS 111. The same urgency applies to someone who has had close contact with measles and is under 1 year old, pregnant, has a weakened immune system, or has not had 2 doses of the MMR or MMRV vaccine. For suspected rubella the NHS advises calling a GP, and says to call a midwife, maternity unit or GP immediately if pregnant with a new rash or after close contact with someone who has rubella.

Because both illnesses are infectious, it is best to call the surgery before going in so that they can arrange a phone consultation or a separate area. Call 999 or go to A&E if someone with measles has a seizure, severe difficulty breathing, cannot stay awake, becomes suddenly confused, is limp or floppy, has a rash that does not fade under a glass, or has a stiff neck or finds light painful.

Rashes in children have many causes, and the NHS itself directs readers with an unexplained rash to its wider rash guide. A clinician usually weighs the whole picture: the pattern and timing of the illness, how unwell the person is, whether there has been contact with a known case, and vaccination history. The NHS points out that it is unlikely to be either illness in someone who has had both doses of the MMRV or MMR vaccine or who has had the infection before.

Where the diagnosis matters for public health or pregnancy, a clinician may arrange laboratory confirmation; the NHS pages do not set out the details, so your own GP or the local health protection team will advise on what is needed.

The MMRV vaccine is offered to all young children in the UK, according to the NHS, and the MMR vaccine is recommended for adults and older children who were not vaccinated when younger. Your GP can vaccinate you for free on the NHS, and the surgery can help you check whether you or your child have had it. The NHS notes that MMR is not suitable if you are pregnant, so vaccination is best checked before pregnancy.