DEAR DR. ROACH: I am hoping you can clarify a lot of conflicting information regarding shingles. I know it is contagious, but can you actually catch shingles from a person? If you never had chickenpox or the vaccine, would you catch shingles or chickenpox?

During an outbreak, how does a caregiver protect him- or herself from catching the virus? Does the chickenpox vaccine make a person more vulnerable to shingles at an earlier age? Many younger people are starting to get shingles. Is the shingles vaccine effective for people over age 60? How about 90 to 100? — J.L.

ANSWER: Shingles is a recurrence of the chickenpox virus (also called varicella-zoster virus), which lies dormant in every person who has had chickenpox or the live chickenpox vaccine. Shingles is nowhere near as contagious as chickenpox, which is found in respiratory secretions, but it is contagious to people who are not immune.

Natural infection from chickenpox or the vaccine makes a person immune. Two doses of the vaccine are about 94% effective in conferring immunity. Thus, a few people who got the vaccine might still catch chickenpox (not shingles) after exposure to shingles. Most adults (98%) in the U.S. are immune. Professional caregivers are encouraged to have immunity proven by blood testing and to be vaccinated if not immune.

People who had the chickenpox vaccine as children are actually LESS likely to develop shingles in the future than those who got a natural infection. This makes sense because the vaccine is a weakened strain. Nonetheless, the new shingles vaccine (Shingrix) is recommended for people whether or not they received the vaccine, and whether or not they recall an episode of chickenpox, which can be missed, especially at a young age.

In the two trials of Shingrix, 13% of the study participants were over 80, and the vaccine had the same effectiveness in this older group compared with the overall group. Those over 90 were not reported separately. The vaccine is recommended for people age 50 and over. Adverse reactions were less common in those who are older (over 70) compared with younger (50 to 69 years old), so I would still likely recommend a shingles vaccine to a person in their 90s. Shingles can have devastating complications, especially in the oldest old.

DEAR DR. ROACH: I was interested in reading your recent column on the causes of psoriasis. My mother suffered from it since the age of 9. It was on her legs, elbows, head and pubic area. I cannot stress enough the influence of stress on this condition. When she was quite old with dementia (perhaps Alzheimer’s?) and she had no stress and no memory, her lifelong psoriasis completely vanished. — B.A.S.

ANSWER: Thank you for writing, and I think it is fascinating that your mother’s psoriasis went away. One type of psoriasis — called “guttate,” which means “droplike” — can sometimes go away after a few months, but resolution after a lifelong course is not something I have read about. A brief search of studies did not reveal a correlation with dementia. I am curious if others, especially my dermatology colleagues, have clinical experience with this. If so, please write to me.